netfilter: ipset: fix return code for destroy when sets are in use

Signed-off-by: NJozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

net/netfilter/ipset/ip_set_core.c

@@ -776,7 +776,7 @@ ip_set_destroy(struct sock *ctnl, struct sk_buff *skb,
 	if (!attr[IPSET_ATTR_SETNAME]) {
 		for (i = 0; i < ip_set_max; i++) {
 			if (ip_set_list[i] != NULL && ip_set_list[i]->ref) {
-				ret = IPSET_ERR_BUSY;
+				ret = -IPSET_ERR_BUSY;
 				goto out;
 			}
 		}