!1698 FIX：修改计算偏移量的实现方法

Merge pull request !1698 from cheng_jinsong/0116

services/param/watcher/proxy/watcher_manager.h

@@ -146,8 +146,7 @@ public:
     static WatcherNodePtr GetNextFromList(ListHeadPtr list, uint32_t nodeId);
     static WatcherNodePtr ConvertNodeToBase(ListNodePtr node)
     {
-        WatcherNodePtr tmp = nullptr;
-        return reinterpret_cast<WatcherNodePtr >((char *)node - (char *)tmp->GetListNode());
+        return reinterpret_cast<WatcherNodePtr >((char *)node - (char*)(&(((WatcherNodePtr)0)->node_)));
     }
     ListNodePtr GetListNode()
     {