py/objstr: Convert mp_uint_t to size_t (and use int) where appropriate.
diff --git a/py/objstrunicode.c b/py/objstrunicode.c
index 8444a26..0091edd 100644
--- a/py/objstrunicode.c
+++ b/py/objstrunicode.c
@@ -284,7 +284,7 @@
     mp_obj_base_t base;
     mp_fun_1_t iternext;
     mp_obj_t str;
-    mp_uint_t cur;
+    size_t cur;
 } mp_obj_str_it_t;
 
 STATIC mp_obj_t str_it_iternext(mp_obj_t self_in) {