avoid leaking crdp for failed path

[ Comment: now that set_cpu_call_rcu_data() is not racy and detects
  overwrites, we can effectively trust its return value and free the
  crdp if already set. ]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>