drm/mediatek: Add fb swap in async_update

Besides x, y position, width and height,
fb also need updating in async update.

Fixes: 920fffcc ("drm/mediatek: update cursors by using async atomic update")
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_drm_plane.c

@@ -121,6 +121,7 @@ static void mtk_plane_atomic_async_update(struct drm_plane *plane,
 	plane->state->src_y = new_state->src_y;
 	plane->state->src_h = new_state->src_h;
 	plane->state->src_w = new_state->src_w;
+	swap(plane->state->fb, new_state->fb);
 	state->pending.async_dirty = true;
 
 	mtk_drm_crtc_async_update(new_state->crtc, plane, new_state);