block: check for an unchanged elevator earlier in __elevator_change

No need to find the actual elevator_type struct for this comparism,
the name is all that is needed.
Signed-off-by: Jinlong Chen <nickyc975@zju.edu.cn>
[hch: split from a larger patch]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221020064819.1469928-4-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/elevator.c

@@ -751,16 +751,13 @@ static int elevator_change(struct request_queue *q, const char *elevator_name)
 		return elevator_switch(q, NULL);
 	}
 
+	if (q->elevator && elevator_match(q->elevator->type, elevator_name, 0))
+		return 0;
+
 	e = elevator_get(q, elevator_name, true);
 	if (!e)
 		return -EINVAL;
 
-	if (q->elevator &&
-	    elevator_match(q->elevator->type, elevator_name, 0)) {
-		elevator_put(e);
-		return 0;
-	}
-
 	return elevator_switch(q, e);
 }