netfilter: nf_conntrack: checking for IS_ERR() instead of NULL

We recently changed this from nf_conntrack_alloc() to nf_ct_tmpl_alloc()
so the error handling needs to changed to check for NULL instead of
IS_ERR().

Fixes: 0838aa7fcfcd ('netfilter: fix netns dependencies with conntrack templates')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index 71f1e9f..d7f1685 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -353,10 +353,8 @@
 	int err = -ENOMEM;
 
 	ct = nf_ct_tmpl_alloc(net, 0, GFP_KERNEL);
-	if (IS_ERR(ct)) {
-		err = PTR_ERR(ct);
+	if (!ct)
 		goto err1;
-	}
 
 	if (!nfct_seqadj_ext_add(ct))
 		goto err2;