drm/i915: Silence sparse over non-static local structure.

drivers/gpu/drm/i915/i915_drv.c|485 col 25| warning: symbol 'i915_pm_ops' was not declared. Should it be static?

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>