drm/i915: LVDS fallback to fixed-mode if EDID not present

Use the recorded panel fixed-mode to populate the get_modes() request in
the absence of an EDID.

Fixes regression from
commit 9cd300e0
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Fri Oct 19 14:51:52 2012 +0300

    drm/i915: Move cached EDID to intel_connector

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
[danvet: Drop the retval-changing hunk, as suggested by Jani in his
review and acked by Chris.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>