ShellPkg/UefiShellAcpiViewCommandLib: Fix VS tool chain build failure

ShellPkg/UefiShellAcpiViewCommandLib: Fix VS tool chain build failure

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1491

This patch is to update the data type of variable "Offset"
from UINT8 to UINT32 to fix following build issue.

...\Parsers\Pptt\PpttParser.c(193): error C2220:
warning treated as error - no 'object' file generated
...\Parsers\Pptt\PpttParser.c(193): warning C4244: '=':
conversion from 'UINT32' to 'UINT8', possible loss of data

Cc: Krzysztof Koch <krzysztof.koch@arm.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>