Elm test dnd: Fixed substraction of void *.

This is not allowed. The pointers need to be cast to char * before doing
pointer arithmetics.

legacy/elementary/src/bin/test_dnd.c

@@ -46,7 +46,7 @@ static Ecore_Timer *_5s_timeout = NULL;
 static int
 _item_ptr_cmp(const void *d1, const void *d2)
 {
-   return (d1 - d2);
+   return ((const char *) d1 - (const char *) d2);
 }
 
 static Elm_Genlist_Item_Class *itc1;