vendorcode/amd/agesa: Fix variable length array declaration

Definition of S_PSTATE only allowed PStateStruct[0], while it is
effectively used as a flexible array. Since sizeof(S_PSTATE) is
reduced here by sizeof(S_PSTATE_VALUES), we have to account for
that when calculating PStateLevelingSizeOfBytes.

In S_PSTATE context, PStateStruct[PStateMaxValue] is valid reference.

GCC 7.2.0 warns about an out of bounds array subscript.

```
    CC         libagesa/vendorcode/amd/agesa/f14/Proc/CPU/Feature/cpuPstateLeveling.o
src/vendorcode/amd/agesa/f14/Proc/CPU/Feature/cpuPstateLeveling.c: In function 'PStateLevelingMain':
src/vendorcode/amd/agesa/f14/Proc/CPU/Feature/cpuPstateLeveling.c:524:65: error: array subscript is above array bounds [-Werror=array-bounds]
             PStateBufferPtrTmp->PStateCoreStruct[0].PStateStruct[k].PStateEnable = 0;
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

Change-Id: If9598a951c6b882432689b677a956c44650c7083
Found-by: gcc (Debian 7.2.0-2) 7.2.0
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/21297
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
5 files changed