prints: fix a couple of formatting errors caught by govet

R=rsc, agl, agl1
CC=golang-dev
https://golang.org/cl/4337041

src/cmd/gofix/fix.go

@@ -39,7 +39,7 @@ func rewrite(x interface{}, visit func(interface{})) {
 
 	// everything else just recurses
 	default:
-		panic(fmt.Errorf("unexpected type %T in walk", x, visit))
+		panic(fmt.Errorf("unexpected type %T in walk", x))
 
 	case nil:
 

src/pkg/crypto/ecdsa/ecdsa_test.go

@@ -20,7 +20,7 @@ func testKeyGeneration(t *testing.T, c *elliptic.Curve, tag string) {
 		return
 	}
 	if !c.IsOnCurve(priv.PublicKey.X, priv.PublicKey.Y) {
-		t.Errorf("%s: public key invalid", tag, err)
+		t.Errorf("%s: public key invalid: %s", tag, err)
 	}
 }