ACPICA: Results from Clang

ACPICA commit 1f08279b3eb13f17004159c28c391a390cd68feb

Changes/fixes From Clang V5.0.1.  Mostly "set but never read"
warnings.

Link: https://github.com/acpica/acpica/commit/1f08279b


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>