md/raid5: call roundup_pow_of_two in raid5_run

Let's call roundup_pow_of_two here instead of open code.
Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/raid5.c

@@ -7732,10 +7732,7 @@ static int raid5_run(struct mddev *mddev)
 		 * discard data disk but write parity disk
 		 */
 		stripe = stripe * PAGE_SIZE;
-		/* Round up to power of 2, as discard handling
-		 * currently assumes that */
-		while ((stripe-1) & stripe)
-			stripe = (stripe | (stripe-1)) + 1;
+		stripe = roundup_pow_of_two(stripe);
 		mddev->queue->limits.discard_alignment = stripe;
 		mddev->queue->limits.discard_granularity = stripe;