workqueue: Use list_last_entry() to get the last idle worker

It is clearer than open code.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -2904,7 +2904,7 @@ static void idle_worker_timeout(struct timer_list *t)
 		unsigned long expires;
 
 		/* idle_list is kept in LIFO order, check the last one */
-		worker = list_entry(pool->idle_list.prev, struct worker, entry);
+		worker = list_last_entry(&pool->idle_list, struct worker, entry);
 		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
 		do_cull = !time_before(jiffies, expires);
 
@@ -2946,7 +2946,7 @@ static void idle_cull_fn(struct work_struct *work)
 		struct worker *worker;
 		unsigned long expires;
 
-		worker = list_entry(pool->idle_list.prev, struct worker, entry);
+		worker = list_last_entry(&pool->idle_list, struct worker, entry);
 		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
 
 		if (time_before(jiffies, expires)) {