NetworkPkg/TcpDxe: Fix GCC build failure

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Zhang Lubo <lubo.zhang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>

NetworkPkg/TcpDxe/SockImpl.c

@@ -593,12 +593,10 @@ SockCancelToken (
 {
   EFI_STATUS     Status;
   LIST_ENTRY     *Entry;
-  LIST_ENTRY     *Next;
   SOCK_TOKEN     *SockToken;
 
   Status    = EFI_SUCCESS;
   Entry     = NULL;
-  Next      = NULL;
   SockToken = NULL;
 
   if (IsListEmpty (SpecifiedTokenList) && Token != NULL) {