workqueue: simplify current_is_workqueue_rescuer()

We can test worker->recue_wq instead of reaching into
current_pwq->wq->rescuer and then comparing it to self.

tj: Commit message.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -3936,7 +3936,7 @@ bool current_is_workqueue_rescuer(void)
 {
 	struct worker *worker = current_wq_worker();
 
-	return worker && worker == worker->current_pwq->wq->rescuer;
+	return worker && worker->rescue_wq;
 }
 
 /**