Fix Python build for activation_soft_max function

[aisk]

There is a function overload for ActivationSoftmax, so the Python build will encounter this error:

 C:\Users\xxxxx\Source\DirectML\Python\src\module.cpp(557,12): error C2672: 'pybind11::module_::def': no matching overloaded function found [C:\Users\xxxxx\Source\DirectML\Python\build\temp.win-amd64-cpython-310\Release\pydirectml.vcxproj] C:\Users\xxxxx\Source\DirectML\Python\pybind11\include\pybind11\pybind11.h(1162,14): could be 'pybind11::module_ &pybind11::module_::def(const char *,Func &&,const Extra ...)' C:\Users\xxxxx\Source\DirectML\Python\src\module.cpp(557,12): 'pybind11::module_ &pybind11::module_::def(const char *,Func &&,const Extra ...)': could not deduce template argument for 'Func'