drm/rockchip: vop: Don't crash for invalid duplicate_state()

It's possible for users to try to duplicate the CRTC state even when the
state doesn't exist. drm_atomic_helper_crtc_duplicate_state() (and other
users of __drm_atomic_helper_crtc_duplicate_state()) already guard this
with a WARN_ON() instead of crashing, so let's do that here too.

Fixes: 4e257d9e ("drm/rockchip: get rid of rockchip_drm_crtc_mode_config")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220617172623.1.I62db228170b1559ada60b8d3e1637e1688424926@changeid

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -1572,6 +1572,9 @@ static struct drm_crtc_state *vop_crtc_duplicate_state(struct drm_crtc *crtc)
 {
 	struct rockchip_crtc_state *rockchip_state;
 
+	if (WARN_ON(!crtc->state))
+		return NULL;
+
 	rockchip_state = kzalloc(sizeof(*rockchip_state), GFP_KERNEL);
 	if (!rockchip_state)
 		return NULL;