[GENETLINK]: Correctly report errors while registering a multicast group

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 457a287..8c11ca4 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -196,7 +196,7 @@
 	genl_ctrl_event(CTRL_CMD_NEWMCAST_GRP, grp);
  out:
 	genl_unlock();
-	return 0;
+	return err;
 }
 EXPORT_SYMBOL(genl_register_mc_group);