typesafe_cb: Fix warnings with gcc-4.5:

Test compiled with warnings:
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c: In function ‘main’:
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:18:2: warning: taking address of expression of type ‘void’
/home/rusty/devel/cvs/ccan/ccan/typesafe_cb/test/compile_ok-typesafe_cb-NULL.c:19:2: warning: taking address of expression of type ‘void’

ccan/typesafe_cb/typesafe_cb.h

@@ -107,7 +107,7 @@
  *		_register_callback(typesafe_cb_def(void, (fn), (arg)), (arg))
  */
 #define typesafe_cb_def(rtype, fn, arg)			\
-	cast_if_any(rtype (*)(void *), (fn), &*(fn),	\
+	cast_if_any(rtype (*)(void *), (fn), (fn)+0,	\
 		    rtype (*)(typeof(*arg)*),		\
 		    rtype (*)(const typeof(*arg)*),	\
 		    rtype (*)(volatile typeof(*arg)*))
@@ -127,7 +127,7 @@
  *		_register_callback(typesafe_cb_exact(void, (fn), (arg)), (arg))
  */
 #define typesafe_cb_exact(rtype, fn, arg)				\
-	cast_if_type(rtype (*)(void *), (fn), &*(fn), rtype (*)(typeof(arg)))
+	cast_if_type(rtype (*)(void *), (fn), (fn)+0, rtype (*)(typeof(arg)))
 
 /**
  * typesafe_cb_const - cast a const callback function if it matches the arg
@@ -166,7 +166,7 @@
  *				   (arg))
  */
 #define typesafe_cb_preargs(rtype, fn, arg, ...)			\
-	cast_if_type(rtype (*)(__VA_ARGS__, void *), (fn), &*(fn),	\
+	cast_if_type(rtype (*)(__VA_ARGS__, void *), (fn), (fn)+0,	\
 		     rtype (*)(__VA_ARGS__, typeof(arg)))
 
 /**
@@ -185,7 +185,7 @@
  *				   (arg))
  */
 #define typesafe_cb_postargs(rtype, fn, arg, ...)			\
-	cast_if_type(rtype (*)(void *, __VA_ARGS__), (fn), &*(fn),	\
+	cast_if_type(rtype (*)(void *, __VA_ARGS__), (fn), (fn)+0,	\
 		     rtype (*)(typeof(arg), __VA_ARGS__))
 
 /**
@@ -210,7 +210,7 @@
  *			  typesafe_cb_cmp(int, (cmpfn), (base)), (arg))
  */
 #define typesafe_cb_cmp(rtype, cmpfn, arg)				\
-	cast_if_type(rtype (*)(const void *, const void *), (cmpfn), &*(cmpfn), \
+	cast_if_type(rtype (*)(const void *, const void *), (cmpfn), (cmpfn)+0, \
 		     rtype (*)(const typeof(*arg)*, const typeof(*arg)*))
 		     
 #endif /* CCAN_CAST_IF_TYPE_H */