drm/rockchip: vop: Fix a dereferenced before check warning

The 'state' can't be NULL, we should check crtc_state.

Fix warning:
drivers/gpu/drm/rockchip/rockchip_drm_vop.c:1096
vop_plane_atomic_async_check() warn: variable dereferenced before check
'state' (see line 1077)

Fixes: 5ddb0bd ("drm/atomic: Pass the full state to planes async atomic check and update")
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20241021072818.61621-1-andyshrk@163.com

Author: Andy Yan

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -1093,10 +1093,10 @@ static int vop_plane_atomic_async_check(struct drm_plane *plane,
 	if (!plane->state->fb)
 		return -EINVAL;
 
-	if (state)
-		crtc_state = drm_atomic_get_existing_crtc_state(state,
-								new_plane_state->crtc);
-	else /* Special case for asynchronous cursor updates. */
+	crtc_state = drm_atomic_get_existing_crtc_state(state, new_plane_state->crtc);
+
+	/* Special case for asynchronous cursor updates. */
+	if (!crtc_state)
 		crtc_state = plane->crtc->state;
 
 	return drm_atomic_helper_check_plane_state(plane->state, crtc_state,