Btrfs: fix path leakage on subvol deletion

The delayed ref patch accidently removed the btrfs_free_path in
btrfs_unlink_subvol, this puts it back and means we don't leak a path.  Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>

fs/btrfs/inode.c

@@ -3076,6 +3076,7 @@ int btrfs_unlink_subvol(struct btrfs_trans_handle *trans,
 	ret = btrfs_update_inode(trans, root, dir);
 	BUG_ON(ret);
 
+	btrfs_free_path(path);
 	return 0;
 }