drm/zte: Stop consulting plane->crtc

We want to get rid of plane->crtc on atomic drivers. Stop looking at it.

v2: Use old_state->crtc (Maarten)
v3: s/fb/crtc/ in commit message to actually match the patch (Shawn)

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326121442.32009-1-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/zte/zx_vou.c

@@ -627,9 +627,10 @@ void zx_vou_layer_enable(struct drm_plane *plane)
 	zx_writel_mask(vou->osd + OSD_CTRL0, bits->enable, bits->enable);
 }
 
-void zx_vou_layer_disable(struct drm_plane *plane)
+void zx_vou_layer_disable(struct drm_plane *plane,
+			  struct drm_plane_state *old_state)
 {
-	struct zx_crtc *zcrtc = to_zx_crtc(plane->crtc);
+	struct zx_crtc *zcrtc = to_zx_crtc(old_state->crtc);
 	struct zx_vou_hw *vou = zcrtc->vou;
 	struct zx_plane *zplane = to_zx_plane(plane);
 	const struct vou_layer_bits *bits = zplane->bits;