drm/i915: Fix up some stray to_i915(dev) after a recent merge

The merge conflict resolution caused some dev->dev_private to return
from the dead. Kill them with to_i915().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1469644349-24571-1-git-send-email-chris@chris-wilson.co.uk


Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>