MdeModulePkg/TerminalDxe: Fix IA32 VS2015x86 build break

MdeModulePkg/TerminalDxe: Fix IA32 VS2015x86 build break

https://bugzilla.tianocore.org/show_bug.cgi?id=190

The issue is with signed/unsigned comparisons between
Mode->CursorRow and Row and Mode->CursorColumn and Column.

The fix is to add typecast to UINTN for comparisons.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Brian Johnson <bjohnson@sgi.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Brian Johnson <bjohnson@sgi.com>