MdeModulePkg: Use IsZeroGuid API for zero GUID checking

Instead of comparing a GUID with gZeroGuid via the CompareGuid API, the
commit uses the IsZeroGuid API to check if the given GUID is a zero GUID.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@Intel.com>