bpo-29676: fix lsprof can't profile C method call. (GH523)

When LOAD_METHOD is used for calling C mehtod, PyMethodDescrObject
was passed to profilefunc from 5566bbb.
But lsprof traces only PyCFunctionObject. Additionally, there can be
some third party extension which assumes passed arg is
PyCFunctionObject without calling PyCFunction_Check().

So make PyCFunctionObject from PyMethodDescrObject when
tstate->c_profilefunc is set.