fix compile error

[typhoonzero]

Fix #5159

[Xreki]

LGTM

[luotao1]

[16:31:20]	The following tests FAILED:
[16:31:20]	167 - test_auc_op (Failed)
[16:31:20]	193 - test_huber_loss_op (Failed)
[16:31:20]	219 - test_lstm_unit_op (Failed)

[typhoonzero]

@luotao1 I reruned the CI job.

[Xreki]

test_auc_op also fails on my computer, you need to add the following function to auc_op:

 protected:
  // CrossEntropy's data type just determined by "X"
  framework::DataType IndicateDataType(
      const framework::ExecutionContext& ctx) const override {
    return framework::ToDataType(ctx.Input<Tensor>("Inference")->type());
  }

I tried to add this function, but it still failed.

235: ERROR: test_check_output (__main__.TestAucOp)
235: ----------------------------------------------------------------------
235: Traceback (most recent call last):
235:   File "test_auc_op.py", line 62, in test_check_output
235:     self.check_output()
235:   File "/home/liuyiqun01/github/Paddle/python/paddle/v2/framework/tests/op_test.py", line 315, in check_output
235:     self.check_output_with_place(place, atol)
235:   File "/home/liuyiqun01/github/Paddle/python/paddle/v2/framework/tests/op_test.py", line 261, in check_output_with_place
235:     outs = exe.run(program, feed=feed_map, fetch_list=fetch_list)
235:   File "/home/liuyiqun01/github/Paddle/build_paddle/build/python/build/lib-python/paddle/v2/framework/executor.py", line 65, in run
235:     self.executor.run(program.desc, scope, 0)
235: EnforceNotMet: Cannot get size of type b at [/home/liuyiqun01/github/Paddle/paddle/framework/tensor_impl.h:57]

[Xreki]

LGTM