py: Change type of .make_new and .call args: mp_uint_t becomes size_t.

This patch changes the type signature of .make_new and .call object method
slots to use size_t for n_args and n_kw (was mp_uint_t.  Makes code more
efficient when mp_uint_t is larger than a machine word.  Doesn't affect
ports when size_t and mp_uint_t have the same size.
diff --git a/py/objzip.c b/py/objzip.c
index 3ac6af1..4b240fb 100644
--- a/py/objzip.c
+++ b/py/objzip.c
@@ -36,7 +36,7 @@
     mp_obj_t iters[];
 } mp_obj_zip_t;
 
-STATIC mp_obj_t zip_make_new(mp_obj_t type_in, mp_uint_t n_args, mp_uint_t n_kw, const mp_obj_t *args) {
+STATIC mp_obj_t zip_make_new(mp_obj_t type_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     mp_arg_check_num(n_args, n_kw, 0, MP_OBJ_FUN_ARGS_MAX, false);
 
     mp_obj_zip_t *o = m_new_obj_var(mp_obj_zip_t, mp_obj_t, n_args);