UefiCpuPkg/PiSmmCpuDxeSmm: Correct the Cr3 typo

UefiCpuPkg/PiSmmCpuDxeSmm: Correct the Cr3 typo

Change the variable name from mInternalGr3 to mInternalCr3.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3015

Signed-off-by: Sheng Wei <w.sheng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>