drm/i915/opregion: don't pretend we did something when we didn't

In theory, the BIOS should not even request these from us now that we
aren't claiming we support these, but when it does anyway, don't pretend it
succeeded. It should be the right thing to do, but might confuse the BIOS.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>