nl80211: don't kfree() ERR_PTR() value

When parse_acl_data() fails, we get an ERR_PTR() value and
then "goto out;", in this case we'd attempt to kfree() it.
Fix that.

Fixes: 9e263e193a ("nl80211: don't put struct cfg80211_ap_settings on stack")
Link: https://lore.kernel.org/r/20210927134402.86c5ae06c952.Ic51e234d998b9045665e5ff8b6db7e29f25d70c0@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -5507,6 +5507,7 @@ static int nl80211_start_ap(struct sk_buff *skb, struct genl_info *info)
 		params->acl = parse_acl_data(&rdev->wiphy, info);
 		if (IS_ERR(params->acl)) {
 			err = PTR_ERR(params->acl);
+			params->acl = NULL;
 			goto out;
 		}
 	}