ACPICA: Add a comment, no functional change

ACPICA commit d586c29a026a6172c1113df4d75fd6d764196e77

Describe 2nd byte of the end_tag resource descriptor.

Link: https://github.com/acpica/acpica/commit/d586c29a


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>