ACPICA: Rename a global variable, no functional change

ACPICA commit ab9c83985e8b2b25dc1c173b753280a8d04922b5

Rename to add the standard prefix for globals.

Link: https://github.com/acpica/acpica/commit/ab9c8398


Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>