drm/i915: Use the plane state for cursor updates.

Cursor planes grab the state from plane->state instead of the state
that was passed. The only updates are atomic now, so use the plane_state
that's passed in.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452164052-21752-6-git-send-email-maarten.lankhorst@linux.intel.com


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>