correct a data type error.

Contributed-under: TianoCore Contribution Agreement 1.0

Signed-off-by: Dong Guo <guo.dong@intel.com>
Reviewed-by: Dong Eric <eric.dong@intel.com>
Reviewed-by: Long Qin <qin.long@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16498 6f19259b-4bc3-4df7-8a09-765794883524