Add TODO in the GRU Operator related

paddle/operators/math/detail/gru_kernel.h

@@ -17,6 +17,7 @@ limitations under the License. */
 
 #include <type_traits>
 
+// TODO(guosheng): refine code style in gru_kernel
 namespace paddle {
 namespace operators {
 namespace math {

paddle/operators/math/gru_compute.h

@@ -19,6 +19,7 @@ namespace paddle {
 namespace operators {
 namespace math {
 
+// TODO(guosheng): refine code style in gru_compute
 template <typename T>
 struct hl_gru_value {
   T *gateWeight;