amd/cimx: fix sb(8|9)00 NULL type redefine

It is inappropriate for chipset code to be redefining
types -- especially NULL to a non-pointer type. There's
only one non-straight forward change. A condition
being checked was '!ptr_type == NULL' (0 as int). That
check is actually 'ptr_type != NULL'.

Change-Id: Iab5733e5a573baba6fec94e0c955ba4fad72c836
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5088
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
diff --git a/src/southbridge/amd/cimx/sb800/SBPLATFORM.h b/src/southbridge/amd/cimx/sb800/SBPLATFORM.h
index fa7d196..ea3f719 100644
--- a/src/southbridge/amd/cimx/sb800/SBPLATFORM.h
+++ b/src/southbridge/amd/cimx/sb800/SBPLATFORM.h
@@ -24,11 +24,7 @@
 #ifndef  _AMD_SBPLATFORM_H_
 #define  _AMD_SBPLATFORM_H_
 
-//#include "cbtypes.h"
-#ifdef NULL
-  #undef NULL
-#endif
-#define NULL            0
+#include <stddef.h>
 
 typedef unsigned long long PLACEHOLDER;