drm/i915/sdvo: Use &intel_sdvo->ddc instead of intel_sdvo->i2c for DDC.

In intel_sdvo_get_lvds_modes() the wrong i2c adapter record is used
for DDC. Thus the code will always have to rely on a LVDS panel
mode supplied by VBT.
In most cases this succeeds, so this didn't get detected for quite
a while.

This regression seems to have been introduced in

commit f899fc64
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Jul 20 15:44:45 2010 -0700

    drm/i915: use GMBUS to manage i2c links

Signed-off-by: Egbert Eich <eich@suse.de>
Cc: stable@vger.kernel.org
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Add note about which commit likely introduced this issue.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>