drm/i915/opregion: fix build error on CONFIG_ACPI=n

drm/i915/opregion: fix build error on CONFIG_ACPI=n

Fix CONFIG_ACPI=n build fail

  CC      drivers/gpu/drm/i915/intel_opregion.o
drivers/gpu/drm/i915/intel_opregion.c: In function ‘intel_opregion_setup’:
drivers/gpu/drm/i915/intel_opregion.c:879:2: error: ‘asle_work’ undeclared (first use in this function)
drivers/gpu/drm/i915/intel_opregion.c:879:2: note: each undeclared identifier is reported only once for each function it appears in
make[4]: *** [drivers/gpu/drm/i915/intel_opregion.o] Error 1

introduced in
commit cb82090a89d1ffcd785b1ea9216922b601087ba7
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Thu Oct 31 18:55:48 2013 +0200

    drm/i915: move opregion asle request handling to a work queue

Reported-by: Jim Davis <jim.epost@gmail.com>
Reference: http://lkml.kernel.org/r/CA+r1ZhjcFpr5KKVX0pLCOP8cAyZoiYO=UyqYMJtNSV-Kt_p7xQ@mail.gmail.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>