dbus: Don't return value from void function

Just discard the value, rather than trying to return a value from a void
function.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/dbus.c

@@ -398,7 +398,7 @@ void weston_dbus_remove_match_signal(DBusConnection *c, const char *sender,
 				     const char *iface, const char *member,
 				     const char *path)
 {
-	return weston_dbus_remove_match(c,
+	weston_dbus_remove_match(c,
 				 "type='signal',"
 				 "sender='%s',"
 				 "interface='%s',"