dm-raid: don't set io_min and io_opt for raid1

These commands
 modprobe brd rd_size=1048576
 vgcreate vg /dev/ram*
 lvcreate -m4 -L10 -n lv vg
trigger the following warnings:
device-mapper: table: 252:10: adding target device (start sect 0 len 24576) caused an alignment inconsistency
device-mapper: table: 252:10: adding target device (start sect 0 len 24576) caused an alignment inconsistency

The warnings are caused by the fact that io_min is 512 and physical block
size is 4096.

If there's chunk-less raid, such as raid1, io_min shouldn't be set to zero
because it would be raised to 512 and it would trigger the warning.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: stable@vger.kernel.org

Author: Mikulas Patocka

drivers/md/dm-raid.c

@@ -3813,8 +3813,10 @@ static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	struct raid_set *rs = ti->private;
 	unsigned int chunk_size_bytes = to_bytes(rs->md.chunk_sectors);
 
-	limits->io_min = chunk_size_bytes;
-	limits->io_opt = chunk_size_bytes * mddev_data_stripes(rs);
+	if (chunk_size_bytes) {
+		limits->io_min = chunk_size_bytes;
+		limits->io_opt = chunk_size_bytes * mddev_data_stripes(rs);
+	}
 }
 
 static void raid_presuspend(struct dm_target *ti)