extmod/modussl_axtls: Use MP_ROM_PTR for objects in allowed args array.

extmod/modussl_axtls.c

@@ -230,10 +230,10 @@ STATIC const mp_obj_type_t ussl_socket_type = {
 STATIC mp_obj_t mod_ssl_wrap_socket(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     // TODO: Implement more args
     static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_key, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} },
-        { MP_QSTR_cert, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} },
+        { MP_QSTR_key, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} },
+        { MP_QSTR_cert, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} },
         { MP_QSTR_server_side, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
-        { MP_QSTR_server_hostname, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_none} },
+        { MP_QSTR_server_hostname, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} },
     };
 
     // TODO: Check that sock implements stream protocol