WUtil: Marked args as unused for compiler in a callback functions

As callback have a fixed prototype, it can be correct to not use all the
arguments, so this patch adds the appropriate stuff to avoid a false
report from compiler.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

WINGs/userdefaults.c

@@ -136,6 +136,9 @@ static void synchronizeUserDefaults(void *foo)
 {
 	UserDefaults *database = sharedUserDefaults;
 
+	/* Parameter not used, but tell the compiler that it is ok */
+	(void) foo;
+
 	while (database) {
 		if (!database->dontSync)
 			WMSynchronizeUserDefaults(database);