netfilter: nft_inner: fix IS_ERR() vs NULL check

The __nft_expr_type_get() function returns NULL on error.  It never
returns error pointers.

Fixes: 3a07327d ("netfilter: nft_inner: support for inner tunnel header matching")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -2873,8 +2873,8 @@ int nft_expr_inner_parse(const struct nft_ctx *ctx, const struct nlattr *nla,
 		return -EINVAL;
 
 	type = __nft_expr_type_get(ctx->family, tb[NFTA_EXPR_NAME]);
-	if (IS_ERR(type))
-		return PTR_ERR(type);
+	if (!type)
+		return -ENOENT;
 
 	if (!type->inner_ops)
 		return -EOPNOTSUPP;