Add DEBUG_ERROR if device fails to subscribe to _deviceTopicIn

Author: pennam

src/ArduinoIoTCloudTCP.cpp

@@ -430,6 +430,7 @@ ArduinoIoTCloudTCP::State ArduinoIoTCloudTCP::handle_SubscribeDeviceTopic()
 
   if (!_mqttClient.subscribe(_deviceTopicIn))
   {
+    DEBUG_ERROR("ArduinoIoTCloudTCP::%s could not subscribe to %s", __FUNCTION__, _deviceTopicIn.c_str());
     return State::SubscribeDeviceTopic;
   }