drm/i915: Fix NULL ptr deref by checking new_crtc_state

intel_atomic_get_new_crtc_state can return NULL, unless crtc state wasn't
obtained previously with intel_atomic_get_crtc_state, so we must check it
for NULLness here, just as in many other places, where we can't guarantee
that intel_atomic_get_crtc_state was called.
We are currently getting NULL ptr deref because of that, so this fix was
confirmed to help.

Fixes: 74a75dc9 ("drm/i915/display: move plane prepare/cleanup to intel_atomic_plane.c")
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230505082212.27089-1-stanislav.lisovskiy@intel.com

drivers/gpu/drm/i915/display/intel_atomic_plane.c

@@ -1029,7 +1029,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
 	int ret;
 
 	if (old_obj) {
-		const struct intel_crtc_state *crtc_state =
+		const struct intel_crtc_state *new_crtc_state =
 			intel_atomic_get_new_crtc_state(state,
 							to_intel_crtc(old_plane_state->hw.crtc));
 
@@ -1044,7 +1044,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
 		 * This should only fail upon a hung GPU, in which case we
 		 * can safely continue.
 		 */
-		if (intel_crtc_needs_modeset(crtc_state)) {
+		if (new_crtc_state && intel_crtc_needs_modeset(new_crtc_state)) {
 			ret = i915_sw_fence_await_reservation(&state->commit_ready,
 							      old_obj->base.resv,
 							      false, 0,