Remove extra semicolon in src/memheap.c

src/memheap.c

@@ -685,7 +685,7 @@ void rt_memheap_free(void *ptr)
 
     if (insert_header)
     {
-        struct rt_memheap_item *n = heap->free_list->next_free;;
+        struct rt_memheap_item *n = heap->free_list->next_free;
 #if defined(RT_MEMHEAP_BEST_MODE)
         rt_size_t blk_size = MEMITEM_SIZE(header_ptr);
         for (;n != heap->free_list; n = n->next_free)