py, unix: Allow to compile with -Wunused-parameter.

See issue #699.
diff --git a/py/objzip.c b/py/objzip.c
index e1bf927..68f9ed3 100644
--- a/py/objzip.c
+++ b/py/objzip.c
@@ -40,7 +40,7 @@
     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);
-    o->base.type = &mp_type_zip;
+    o->base.type = type_in;
     o->n_iters = n_args;
     for (mp_uint_t i = 0; i < n_args; i++) {
         o->iters[i] = mp_getiter(args[i]);