upstream: memleak on error path; found by libfuzzer

OpenBSD-Commit-ID: 34d44cb0fb5bdb5fcbc6b02b804e71b20a7a5fc7
diff --git a/sshsig.c b/sshsig.c
index bda57b3..b993b7c 100644
--- a/sshsig.c
+++ b/sshsig.c
@@ -658,7 +658,7 @@
  fail:
 	if (errstrp != NULL)
 		*errstrp = errstr;
-	free(ret);
+	sshsigopt_free(ret);
 	return NULL;
 }