xen-blkback: Avoid that gcc 7 warns about fall-through when building with W=1

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Roger Pau Monn303251 <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/xen-blkback/blkback.c

@@ -1251,6 +1251,7 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
 		break;
 	case BLKIF_OP_WRITE_BARRIER:
 		drain = true;
+		/* fall through */
 	case BLKIF_OP_FLUSH_DISKCACHE:
 		ring->st_f_req++;
 		operation = REQ_OP_WRITE;

drivers/block/xen-blkback/xenbus.c

@@ -810,7 +810,8 @@ static void frontend_changed(struct xenbus_device *dev,
 		xenbus_switch_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
-		/* fall through if not online */
+		/* fall through */
+		/* if not online */
 	case XenbusStateUnknown:
 		/* implies xen_blkif_disconnect() via xen_blkbk_remove() */
 		device_unregister(&dev->dev);