[IPV6] FIB_RULE: Sparse: fib6_rules_cleanup() is of void.

| net/ipv6/fib6_rules.c:319:2: warning: returning void-valued expression

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c
index cac5807..8d05527 100644
--- a/net/ipv6/fib6_rules.c
+++ b/net/ipv6/fib6_rules.c
@@ -316,5 +316,5 @@
 
 void fib6_rules_cleanup(void)
 {
-	return unregister_pernet_subsys(&fib6_rules_net_ops);
+	unregister_pernet_subsys(&fib6_rules_net_ops);
 }