workqueue: remove useless unlock() and lock() in series

This is no point to unlock() and then lock() the same mutex
back to back.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -4403,13 +4403,11 @@ void destroy_workqueue(struct workqueue_struct *wq)
 		raw_spin_unlock_irq(&pwq->pool->lock);
 	}
 	mutex_unlock(&wq->mutex);
-	mutex_unlock(&wq_pool_mutex);
 
 	/*
 	 * wq list is used to freeze wq, remove from list after
 	 * flushing is complete in case freeze races us.
 	 */
-	mutex_lock(&wq_pool_mutex);
 	list_del_rcu(&wq->list);
 	mutex_unlock(&wq_pool_mutex);