batman-adv: Don't return value in void function

gw_node_delete is defined with "void" as return type, but still tries to
return a value. The called function gw_node_delete is also return as
void and thus doesn't provide a value for us.
Signed-off-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/gateway_client.c

@@ -352,7 +352,7 @@ void gw_node_update(struct bat_priv *bat_priv,
 
 void gw_node_delete(struct bat_priv *bat_priv, struct orig_node *orig_node)
 {
-	return gw_node_update(bat_priv, orig_node, 0);
+	gw_node_update(bat_priv, orig_node, 0);
 }
 
 void gw_node_purge(struct bat_priv *bat_priv)