les: changed if-else blocks to conform with golint (#16658)

les/protocol.go

@@ -160,9 +160,8 @@ func (a *announceData) checkSignature(pubKey *ecdsa.PublicKey) error {
 	pbytes := elliptic.Marshal(pubKey.Curve, pubKey.X, pubKey.Y)
 	if bytes.Equal(pbytes, recPubkey) {
 		return nil
-	} else {
-		return errors.New("Wrong signature")
 	}
+	return errors.New("Wrong signature")
 }
 
 type blockInfo struct {