ACPICA: Remove a redundant cast to acpi_size for ACPI_OFFSET() macro.

It is already casted to acpi_size by ACPI_PTR_DIFF() macro.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>