MdeModulePkg: Fix VS2015 warning C4311 & C4312 in RegularExpressionDxe

MdeModulePkg: Fix VS2015 warning C4311 & C4312 in RegularExpressionDxe

warning C4311: pointer truncation from 'void *' to 'unsigned long'
warning C4312: conversion from 'unsigned long' to 'void *' of greater size
Update code to convert type to UINTN first, then convert it to other type.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Samer El-Haj-Mahmoud <samer.el-haj-mahmoud@hpe.com>
Acked-by: Michael Kinney <michael.d.kinney@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19114 6f19259b-4bc3-4df7-8a09-765794883524