dm mpath: use DM_MAPIO_SUBMITTED instead of magic number 0 in process_queued_bios()

Signed-off-by: Wang Sheng-Hui <shhuiw@foxmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -714,7 +714,7 @@ static void process_queued_bios(struct work_struct *work)
 		case DM_MAPIO_REMAPPED:
 			generic_make_request(bio);
 			break;
-		case 0:
+		case DM_MAPIO_SUBMITTED:
 			break;
 		default:
 			WARN_ONCE(true, "__multipath_map_bio() returned %d\n", r);