sched/wake_q: Clarify queue reinit comment

sched/wake_q: Clarify queue reinit comment

As of:

  3ba76b39ab0 ("locking/rwsem: Reinit wake_q after use")

the comment regarding the list reinitialization no longer applies,
update it with the new wake_q_init() helper.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Waiman Long <longman@redhat.com>
Cc: peterz@infradead.org
Cc: longman@redhat.com
Cc: akpm@linux-foundation.org
Cc: paulmck@linux.vnet.ibm.com
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/20170129151531.GA2444@linux-80c1.suse
Signed-off-by: Ingo Molnar <mingo@kernel.org>