drm/i915: s/crtc_state/old_crtc_state/ in intel_atomic_commit()

Avoid some head spinning by renaming the crtc_state variable to
old_crtc_state.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457543247-13987-6-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>