imsm: FIX: indicate that metadada has to be written

During adding spare disks to raid0, spare metadata is not written.
This is due to exit form sync_metadata() on empty updates_pending flag.

When mdmon is absent indicate sync_metadata() to flush changes to disks.

Signed-off-by: Adam Kwolek <adam.kwolek@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

super-intel.c

@@ -3838,6 +3838,7 @@ static int add_to_super_imsm(struct supertype *st, mdu_disk_info_t *dk,
 	} else {
 		dd->next = super->disks;
 		super->disks = dd;
+		super->updates_pending++;
 	}
 
 	return 0;