dm raid: fix discard limits for raid1

Block core warned that discard_granularity was 0 for dm-raid with
personality of raid1. Reason is that raid_io_hints() was incorrectly
special-casing raid1 rather than raid0.

Fix raid_io_hints() by removing discard limits settings for
raid1. Check for raid0 instead.

Fixes: 61697a6abd24a ("dm: eliminate 'split_discard_bios' flag from DM target interface")
Cc: [e-mail]
Reported-by: Zdenek Kabelac <[e-mail]>
Reported-by: Mikulas Patocka <[e-mail]>
Reported-by: Stephan Bärwolf <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-raid.c

···
 	blk_limits_io_opt(limits, chunk_size_bytes * mddev_data_stripes(rs));
 
 	/*
-	 * RAID1 and RAID10 personalities require bio splitting,
-	 * RAID0/4/5/6 don't and process large discard bios properly.
+	 * RAID0 and RAID10 personalities require bio splitting,
+	 * RAID1/4/5/6 don't and process large discard bios properly.
 	 */
-	if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
+	if (rs_is_raid0(rs) || rs_is_raid10(rs)) {
 		limits->discard_granularity = chunk_size_bytes;
 		limits->max_discard_sectors = rs->md.chunk_sectors;
 	}