__btrfs_abort_transaction doesn't use its root parameter except to
obtain an fs_info pointer.  We can obtain that from trans->root->fs_info
for now and from trans->fs_info in a later patch.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>