remember to return error

Summary:
This bug was created in D60825154

We to return the error
If we do not, we set the client to nil and this results in a nil pointer exception later that was found in production

Reviewed By: yfeldblum

Differential Revision: D64238799

fbshipit-source-id: c05195ca89d9f10c086873e8951e127d2ba44ece

thrift/lib/go/thrift/rocket_rsocket_client.go

@@ -65,7 +65,7 @@ func (r *rsocketClient) SendSetup(serverMetadataPush OnServerMetadataPush) error
 	clientStarter := clientBuilder.Acceptor(acceptor(serverMetadataPush))
 	client, err := clientStarter.Transport(transporter(r.conn)).Start(context.Background())
 	r.client = client
-	return nil
+	return err
 }
 
 func acceptor(onMetadataPush OnServerMetadataPush) func(_ context.Context, socket rsocket.RSocket) rsocket.RSocket {