secmark: do not return early if there was no error

Commit 4a5a5c73 attempted to pass decent error messages back to userspace for
netfilter errors.  In xt_SECMARK.c however the patch screwed up and returned
on 0 (aka no error) early and didn't finish setting up secmark.  This results
in a kernel BUG if you use SECMARK.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: James Morris <jmorris@namei.org>

net/netfilter/xt_SECMARK.c

@@ -101,7 +101,7 @@ static int secmark_tg_check(const struct xt_tgchk_param *par)
 	switch (info->mode) {
 	case SECMARK_MODE_SEL:
 		err = checkentry_selinux(info);
-		if (err <= 0)
+		if (err)
 			return err;
 		break;