netfilter: nf_tables: fix wrong pointer passed to PTR_ERR()

It should be 'chain' passed to PTR_ERR() in the error path
after calling nft_chain_lookup() in nf_tables_delrule().

Fixes: f80a612d ("netfilter: nf_tables: add support to destroy operation")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -3724,7 +3724,7 @@ static int nf_tables_delrule(struct sk_buff *skb, const struct nfnl_info *info,
 		chain = nft_chain_lookup(net, table, nla[NFTA_RULE_CHAIN],
 					 genmask);
 		if (IS_ERR(chain)) {
-			if (PTR_ERR(rule) == -ENOENT &&
+			if (PTR_ERR(chain) == -ENOENT &&
 			    NFNL_MSG_TYPE(info->nlh->nlmsg_type) == NFT_MSG_DESTROYRULE)
 				return 0;