Fix Python compilation

src/python/src/grpc/_adapter/_c/utility.c

@@ -123,7 +123,7 @@ PyObject *pygrpc_consume_event(grpc_event event) {
           event.success ? Py_True : Py_False);
     } else {
       result = Py_BuildValue("iOOONO", GRPC_OP_COMPLETE, tag->user_tag,
-          tag->call ? tag->call : Py_None, Py_None,
+          tag->call ? (PyObject*)tag->call : Py_None, Py_None,
           pygrpc_consume_ops(tag->ops, tag->nops),
           event.success ? Py_True : Py_False);
     }