Executer: Fix trivial issues in AcpiGetSerialAccessBytes().

This patch fixes trivial issues in AcpiGetSerialAccessBytes(), no real
functional bugs. Lv Zheng.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Merge pull request #41 from zetalog/acpica-access

Executer: Fix trivial issues in AcpiGetSerialAccessBytes().