soc/amd/common: Set AltImageBasePtr to 0

In the original AGESA headers, AltImageBasePtr is a UINT32, so don't
set it to VOID.  0 works for either UINT32 or VOID *, as demonstrated
by the other 7 places in this file where it's already set to 0 instead
of NULL.

Change this location to 0 to support either version of the headers.

BUG=b:64766233
TEST=Build in cros tree and upstream coreboot, with old headers
and updated headers.

Change-Id: Ib6f3883e08231a6ca896c2ee2ef631c77feafedd
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/22060
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/soc/amd/common/agesawrapper.c

@@ -122,7 +122,7 @@ AGESA_STATUS agesawrapper_amdinitpost(void)
 
 	AmdParamStruct.AgesaFunctionName = AMD_INIT_POST;
 	AmdParamStruct.AllocationMethod = PreMemHeap;
-	AmdParamStruct.StdHeader.AltImageBasePtr = NULL;
+	AmdParamStruct.StdHeader.AltImageBasePtr = 0;
 	AmdParamStruct.StdHeader.CalloutPtr = &GetBiosCallout;
 	AmdParamStruct.StdHeader.Func = 0;
 	AmdParamStruct.StdHeader.ImageBasePtr = 0;