proto-loader: fix typescript generation callType for client streaming

[badsyntax]

I noticed an unexpected type error with the following code:

const stream = client.clientStreamingCall(
  (error?: grpc.ServiceError) => {
    if (error) {
      console.error(error.message);
    } 
  }
);
// error: expected serverMesage
stream.write({
  clientMessage: 'Message from client',
});

Seems to me stream.write should be writing a request message not a response message.