dm mpath: avoid that building with W=1 causes gcc 7 to complain about fall-through

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -1379,6 +1379,7 @@ static void pg_init_done(void *data, int errors)
 	case SCSI_DH_RETRY:
 		/* Wait before retrying. */
 		delay_retry = 1;
+		/* fall through */
 	case SCSI_DH_IMM_RETRY:
 	case SCSI_DH_RES_TEMP_UNAVAIL:
 		if (pg_init_limit_reached(m, pgpath))