block: invoke blk_mq_exit_sched no matter whether have .exit_sched

We will register debugfs for scheduler no matter whether it have
defined callback funciton .exit_sched. So, blk_mq_exit_sched()
is always needed to unregister debugfs. Also, q->elevator should
be set as NULL after exiting scheduler.

For now, since all register scheduler have defined .exit_sched,
it will not cause any actual problem. But It will be more reasonable
to do this change.

Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/elevator.c b/block/elevator.c
index 90ed7a2..7d76b61 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -191,8 +191,7 @@ static void elevator_release(struct kobject *kobj)
 void __elevator_exit(struct request_queue *q, struct elevator_queue *e)
 {
 	mutex_lock(&e->sysfs_lock);
-	if (e->type->ops.exit_sched)
-		blk_mq_exit_sched(q, e);
+	blk_mq_exit_sched(q, e);
 	mutex_unlock(&e->sysfs_lock);
 
 	kobject_put(&e->kobj);