smack: make smack_parse_opts_str() clean up on failure

fixes e.g. a btrfs leak...

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

security/smack/smack_lsm.c

@@ -735,6 +735,7 @@ out_err:
 	kfree(fshat);
 	kfree(fsroot);
 	kfree(fstransmute);
+	security_free_mnt_opts(opts);
 	return rc;
 }