md/raid10: wait barrier before returning discard request with REQ_NOWAIT

raid10_handle_discard should wait barrier before returning a discard bio
which has REQ_NOWAIT. And there is no need to print warning calltrace
if a discard bio has REQ_NOWAIT flag. Quality engineer usually checks
dmesg and reports error if dmesg has warning/error calltrace.

Fixes: c9aa889 ("md: raid10 add nowait support")
Signed-off-by: Xiao Ni <xni@redhat.com>
Acked-by: Coly Li <colyli@kernel.org>
Link: https://lore.kernel.org/linux-raid/20250306094938.48952-1-xni@redhat.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>

drivers/md/raid10.c

@@ -1624,11 +1624,10 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
 	if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 		return -EAGAIN;
 
-	if (WARN_ON_ONCE(bio->bi_opf & REQ_NOWAIT)) {
+	if (!wait_barrier(conf, bio->bi_opf & REQ_NOWAIT)) {
 		bio_wouldblock_error(bio);
 		return 0;
 	}
-	wait_barrier(conf, false);
 
 	/*
 	 * Check reshape again to avoid reshape happens after checking