fix misuse of typesafe_cb_cast() in example

From 32f86c701ab0e0ad0ad6981314a9bff2dc5ebb74 Mon Sep 17 00:00:00 2001
From: Yubin Ruan <ablacktshirt@gmail.com>
Date: Wed, 14 Mar 2018 11:14:54 +0800
Subject: [PATCH] fix misuse of typesafe_cb_cast() in example
Signed-off-by: Yubin Ruan <ablacktshirt@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/typesafe_cb/typesafe_cb.h

@@ -27,7 +27,7 @@
  *	// We can take either an unsigned long or a void *.
  *	void _set_some_value(void *val);
  *	#define set_some_value(e)			\
- *		_set_some_value(typesafe_cb_cast(void *, (e), unsigned long))
+ *		_set_some_value(typesafe_cb_cast(void *, unsigned long, (e)))
  */
 #define typesafe_cb_cast(desttype, oktype, expr)			\
 	__builtin_choose_expr(						\