Fix fallout from r1021 which caused compile failures if only the dummy programmer was selected

Corresponding to flashrom svn r1026.
Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>

flash.h

@@ -25,6 +25,7 @@
 #define __FLASH_H__ 1
 
 #include <stdint.h>
+#include <stddef.h>
 #include "hwaccess.h"
 #ifdef _WIN32
 #include <windows.h>
@@ -32,10 +33,6 @@
 #undef max
 #endif
 
-#ifndef NULL
-#define NULL ((void *) 0)
-#endif
-
 typedef unsigned long chipaddr;
 
 enum programmer {