drm/i915: fix up adjusted_mode tracking for interlaced modes

With the hw state readout&check code it's important that the values we
keep around are the canonical ones. Unfortunately when adding the pipe
timings readout support I've missed that the write side adjusts the
timings in the pipe config.

Fix this up and so prevent the unsightly WARN noise in dmesg. This
regression has been introduced in

commit 1bd1bd80
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Apr 29 21:56:12 2013 +0200

    drm/i915: hw state readout support for pipe timings

Reported-by: Paulo Zanoni <przanoni@gmail.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>