md: don't impose the MD_SB_DISKS limit on arrays without metadata.

These arrays, created with "mdadm --build" don't benefit from a limit.
The default will be used, which is '0' and is interpreted as "don't
impose a limit".

Reported-by: ian_bruce@mail.ru
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/md.c

@@ -6450,9 +6450,8 @@ static int set_array_info(struct mddev *mddev, mdu_array_info_t *info)
 	mddev->layout        = info->layout;
 	mddev->chunk_sectors = info->chunk_size >> 9;
 
-	mddev->max_disks     = MD_SB_DISKS;
-
 	if (mddev->persistent) {
+		mddev->max_disks = MD_SB_DISKS;
 		mddev->flags = 0;
 		mddev->sb_flags = 0;
 	}