fix unittest. test=develop

paddle/fluid/operators/softmax_with_cross_entropy_op.h

@@ -40,10 +40,12 @@ class SoftmaxWithCrossEntropyKernel : public framework::OpKernel<T> {
     softmax->mutable_data<T>(context.GetPlace());
     loss->mutable_data<T>(context.GetPlace());
 
+    int axis_dim = logits->dims()[logits->dims().size()-1];
+
     auto& dev_ctx =
         context.template device_context<platform::CPUDeviceContext>();
     math::SoftmaxFunctor<platform::CPUDeviceContext, T, false>()(
-        dev_ctx, -1, logits, softmax);
+        dev_ctx, axis_dim, logits, softmax);
     math::CrossEntropyFunctor<platform::CPUDeviceContext, T>()(
         dev_ctx, loss, softmax, labels, context.Attr<bool>("soft_label"),
         context.Attr<int>("ignore_index"));