UefiCpuPkg/MtrrLib/UnitTest: Fix 32-bit GCC build issues

UefiCpuPkg/MtrrLib/UnitTest: Fix 32-bit GCC build issues

When using UT_ASSERT_EQUAL() on a pointer value, it must be
cast to UINTN.  This follows the samples provided with the
UnitTestFrameworkPkg.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>