[ log ] Add error log for setOptimizer failure

- Add ml_loge for setOptimizer failure

Signed-off-by: Eunju Yang <[email protected]>

nntrainer/models/neuralnet.cpp

@@ -1323,6 +1323,7 @@ NeuralNetwork::getUnsortedLayers(const std::string &input_layer,
 int NeuralNetwork::setOptimizer(
   std::shared_ptr<ml::train::Optimizer> optimizer) {
   if (initialized) {
+    ml_loge("Cannot set optimizer if already initialized");
     return ML_ERROR_NOT_SUPPORTED;
   }