Assemble: fix "no uptodate device" message.

Since we introduced replacement devices, the 'i' used in
start_array() is twice the slot number.

So we need to adjust when printing.

Signed-off-by: NeilBrown <neilb@suse.de>

Assemble.c

@@ -984,7 +984,7 @@ static int start_array(int mdfd,
 		} else if (c->verbose > 0 && i < content->array.raid_disks*2
 			   && (i&1) == 0)
 			pr_err("no uptodate device for slot %d of %s\n",
-			       i, mddev);
+			       i/2, mddev);
 	}
 
 	if (content->array.level == LEVEL_CONTAINER) {