netfilter: nf_tables: remove unused variable

Variable 'ext' is being assigned but are never used hence they are
unused and can be removed.

Cleans up clang warnings:
net/netfilter/nf_tables_api.c:4032:28: warning: variable ‘ext’ set but not used [-Wunused-but-set-variable]
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -4029,7 +4029,6 @@ static int nft_get_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			    const struct nlattr *attr)
 {
 	struct nlattr *nla[NFTA_SET_ELEM_MAX + 1];
-	const struct nft_set_ext *ext;
 	struct nft_data_desc desc;
 	struct nft_set_elem elem;
 	struct sk_buff *skb;
@@ -4063,7 +4062,6 @@ static int nft_get_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 		return PTR_ERR(priv);
 
 	elem.priv = priv;
-	ext = nft_set_elem_ext(set, &elem);
 
 	err = -ENOMEM;
 	skb = nlmsg_new(NLMSG_GOODSIZE, GFP_ATOMIC);