proto_handshake: fix clean-up on mkkeys() failure

Reported by:	ChronoNova
Bug bounty:	$10 ("harmless")

Author: gperciva

lib/proto/proto_handshake.c

@@ -293,7 +293,7 @@ handshakedone(struct handshake_cookie * H)
 	/* Perform the final computation. */
 	if (proto_crypt_mkkeys(H->K, H->nonce_local, H->nonce_remote,
 	    H->yh_remote, H->x, H->nopfs, H->decr, &c, &s))
-		goto err0;
+		return (handshakefail(H));
 
 	/* Perform the callback. */
 	rc = (H->callback)(H->cookie, c, s);
@@ -303,10 +303,6 @@ handshakedone(struct handshake_cookie * H)
 
 	/* Return status code from callback. */
 	return (rc);
-
-err0:
-	/* Failure! */
-	return (-1);
 }
 
 /**