btrfs: 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>
Acked-by: David Sterba <dsterba@suse.com>
Link: https://lore.kernel.org/r/20211019062530.2174626-5-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/btrfs/volumes.c

@@ -508,7 +508,7 @@ btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 	}
 
 	if (flush)
-		filemap_write_and_wait((*bdev)->bd_inode->i_mapping);
+		sync_blockdev(*bdev);
 	ret = set_blocksize(*bdev, BTRFS_BDEV_BLOCKSIZE);
 	if (ret) {
 		blkdev_put(*bdev, flags);