MdeModulePkg SmmLockBoxDxeLib: Get SmmCommRegion for COMM buffer

MdeModulePkg SmmLockBoxDxeLib: Get SmmCommRegion for COMM buffer

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=593

Currently, SmmCommunciate fails in RestoreLockBox after
SmmReadyToLock since COMM buffer is in stack instead of
using SmmCommRegion by gEdkiiPiSmmCommunicationRegionTableGuid.

This patch is to get SmmCommRegion by
gEdkiiPiSmmCommunicationRegionTableGuid for COMM buffer

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Baraneedharan Anbazhagan <anbazhagan@hp.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>