drm/i915: use staged outuput config in lvds->mode_fixup

- Use the check_cloned helper from the previous patch.
- Use encoder->new_crtc to check crtc properties.

v2: Kill the double negation with s/!non_cloned/is_cloned, suggested
by Jesse Barnes.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>