netfilter: conntrack: clean up returns in nf_conntrack_log_invalid_sysctl()

Smatch complains that these look like error paths with missing error
codes, especially the one where we return if nf_log_is_registered() is
true:

    net/netfilter/nf_conntrack_standalone.c:575 nf_conntrack_log_invalid_sysctl()
    warn: missing error code? 'ret'

In fact, all these return zero deliberately.  Change them to return a
literal instead which helps readability as well as silencing the warning.

Fixes: e89a680 ("netfilter: load nf_log_syslog on enabling nf_conntrack_log_invalid")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: Dan Carpenter

net/netfilter/nf_conntrack_standalone.c

@@ -567,16 +567,16 @@ nf_conntrack_log_invalid_sysctl(const struct ctl_table *table, int write,
 		return ret;
 
 	if (*(u8 *)table->data == 0)
-		return ret;
+		return 0;
 
 	/* Load nf_log_syslog only if no logger is currently registered */
 	for (i = 0; i < NFPROTO_NUMPROTO; i++) {
 		if (nf_log_is_registered(i))
-			return ret;
+			return 0;
 	}
 	request_module("%s", "nf_log_syslog");
 
-	return ret;
+	return 0;
 }
 
 static struct ctl_table_header *nf_ct_netfilter_header;