xen-blkback: use sync_blockdev

Use sync_blockdev instead of opencoding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20211019062530.2174626-4-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/xen-blkback/xenbus.c

@@ -98,7 +98,7 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
 		return;
 	}
 
-	err = filemap_write_and_wait(blkif->vbd.bdev->bd_inode->i_mapping);
+	err = sync_blockdev(blkif->vbd.bdev);
 	if (err) {
 		xenbus_dev_error(blkif->be->dev, err, "block flush");
 		return;