wfcqueue: Fix lock and unlock functions

The current implementation of cds_wfcq_dequeue_lock() and
cds_wfcq_dequeue_unlock() entails mutually assured recursion.
Redirect to _cds_wfcq_dequeue_lock() and _cds_wfcq_dequeue_unlock(),
respectively.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>