drm/i915: Pass the correct crtc state to .update_plane()

Pass the current crtc state, not the old crtc state, to the
.update_plane() hook.

Noticed on BSW when PRIMSIZE was getting programmed to a stale value
which produced utter garbage on screen eg. wwhen going from 1920x1080
to 1024x768.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: a758e6845825 ("drm/i915: Do not use commit_plane for sprite planes.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457543247-13987-3-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_atomic_plane.c

@@ -195,12 +195,10 @@ static void intel_plane_atomic_update(struct drm_plane *plane,
 	struct intel_plane_state *intel_state =
 		to_intel_plane_state(plane->state);
 	struct drm_crtc *crtc = plane->state->crtc ?: old_state->crtc;
-	struct drm_crtc_state *crtc_state =
-		drm_atomic_get_existing_crtc_state(old_state->state, crtc);
 
 	if (intel_state->visible)
 		intel_plane->update_plane(plane,
-					  to_intel_crtc_state(crtc_state),
+					  to_intel_crtc_state(crtc->state),
 					  intel_state);
 	else
 		intel_plane->disable_plane(plane, crtc);