const dtype is needed.

for example it's needed when inserting cast for target rs6

Author: zhijxu-MS

tf2onnx/graph.py

@@ -414,8 +414,9 @@ def make_const(self, name, np_val, skip_conversion=False, raw=True):
         else:
             onnx_tensor = helper.make_tensor(name, utils.map_numpy_to_onnx_dtype(np_val.dtype),
                                              np_val.shape, np_val, raw=False)
+        dtype = onnx_tensor.data_type
         node = self.make_node("Const", [], outputs=[name], name=name, attr={"value": onnx_tensor},
-                              skip_conversion=skip_conversion)
+                              skip_conversion=skip_conversion, dtypes=[dtype])
         self.set_shape(name, np_val.shape)
         self.set_dtype(name, utils.map_numpy_to_onnx_dtype(np_val.dtype))
         return node