message: Improve Flex delegate error reporting
diff: @@ -39,10 +39,11 @@ TfLiteStatus Prepare(TfLiteContext* context, TfLiteDelegate* delegate) {
  context->recommended_num_threads);
  }
  - if (!reinterpret_cast<DelegateData*>(delegate->data_)
  - ->Prepare(session_options)
  - .ok()) {
  - context->ReportError(context, "Failed to initialize TensorFlow context.");
  + auto status = reinterpret_cast<DelegateData*>(delegate->data_)
  + ->Prepare(session_options);
  + if (!status.ok()) {
  + context->ReportError(context, "Failed to initialize TensorFlow context: %s",
  + status.error_message().c_str());
  return kTfLiteError;
  }
  