xen-blkback: use sync_blockdev

Use sync_blockdev instead of opencoding it.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Chaitanya Kulkarni <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/xen-blkback/xenbus.c

···
 		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;