SecurityPkg Tcg2Dxe: Get correct digest list size

SecurityPkg Tcg2Dxe: Get correct digest list size

Current code uses GetDigestListSize(DigestList) to get
digest list size, that is incorrect.
The code should get digest list size of digests copied
into event2 log, those digests are compacted, so
GetDigestListBinSize() should be used.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Chao Zhang <chao.b.zhang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>