clean: use f(void) instead of f() to declare a pointer to a function without arguments

Explicitly state that menu_item functions like clean_cmd don't take
any arguments by using void instead of an empty parameter list.

Found using gcc -Wstrict-prototypes.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/clean.c

@@ -66,7 +66,7 @@ struct menu_item {
 	char hotkey;
 	const char *title;
 	int selected;
-	int (*fn)();
+	int (*fn)(void);
 };
 
 enum menu_stuff_type {