Avoid compiler warning about unreachable code

Summary:
Fix https://github.com/caffe2/caffe2/issues/764

I don't think we care much about the behavior, exactly, as long as it's a loud clear crash - right?
Closes https://github.com/caffe2/caffe2/pull/766

Differential Revision: D5211826

Pulled By: Yangqing

fbshipit-source-id: 9bb134b387d6620f1235a7b1ddf13092d73ae44c
diff --git a/caffe2/core/operator_schema.h b/caffe2/core/operator_schema.h
index 35362b7..8c5d6f3 100644
--- a/caffe2/core/operator_schema.h
+++ b/caffe2/core/operator_schema.h
@@ -273,7 +273,7 @@
       };
   CostInferenceFunctionType cost_inference_function_ =
       [](const OperatorDef& def, const vector<TensorShape>&) {
-        CAFFE_THROW("No cost inference function registered.");
+        LOG(FATAL) << "No cost inference function registered.";
         return Cost();
       };
   DeviceInferenceFunctionType device_inference_function_ =