DynamicTablesPkg: Fix ACPI table rev field width

DynamicTablesPkg: Fix ACPI table rev field width

The VS2017 compiler reports 'warning C4244: '=': conversion from
'const UINT32' to 'UINT8', possible loss of data' when the ACPI
table revision field is being updated.

The width of the revision field in the EFI_ACPI_DESCRIPTION_HEADER
struct is 8-bit wide. Therefore, to fix the above warning make the
ACPI Table revision field usage 8-bit wide across Dynamic Tables
Framework.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>