If i915 opregion is present, the acpi_video driver doesn't register
itself immediately; it defers that until the i915 opregion code is done.
But if that *fails*, the acpi_video driver was never getting registered.
And thus I have no backlight support on my Lenovo IdeaPad S10-3.

Call acpi_video_register() on the failure path, and it works again.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Matthew Garrett <mjg@redhat.com>