Fix -Walloc-size

GCC 14 introduces a new -Walloc-size included in -Wextra which gives:
```
urcu-call-rcu-impl.h:912:20: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:927:22: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:912:20: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:927:22: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:912:20: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:927:22: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:912:20: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:927:22: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:912:20: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:927:22: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
workqueue.c:401:20: warning: allocation of insufficient size '1' for type 'struct urcu_workqueue_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
workqueue.c:432:14: warning: allocation of insufficient size '1' for type 'struct urcu_workqueue_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:912:20: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion' with size '16' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
urcu-call-rcu-impl.h:927:22: warning: allocation of insufficient size '1' for type 'struct call_rcu_completion_work' with size '24' [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
qsbr.c:49:14: warning: allocation of insufficient size ‘1’ for type ‘struct mynode’ with size ‘40’ [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
mb.c:50:14: warning: allocation of insufficient size ‘1’ for type ‘struct mynode’ with size ‘40’ [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
membarrier.c:50:14: warning: allocation of insufficient size ‘1’ for type ‘struct mynode’ with size ‘40’ [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
signal.c:49:14: warning: allocation of insufficient size ‘1’ for type ‘struct mynode’ with size ‘40’ [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
bp.c:49:14: warning: allocation of insufficient size ‘1’ for type ‘struct mynode’ with size ‘40’ [-Walloc-size[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Walloc-size]]
```

The calloc prototype is:
```
void *calloc(size_t nmemb, size_t size);
```

So, just swap the number of members and size arguments to match the prototype, as
we're initialising 1 struct of size `sizeof(struct ...)`. GCC then sees we're not
doing anything wrong.

Signed-off-by: Sam James <sam@gentoo.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Id84ce5cf9a1b97bfa942597aa188ef6e27e7c10d