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.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
1 file changed