drm/atomic: Don't pollute crtc_state->mode_blob with error pointers

Make sure we don't assign an error pointer to crtc_state->mode_blob
as that will break all kinds of places that assume either NULL or a
valid pointer (eg. drm_property_blob_put()).

Cc: stable@vger.kernel.org
Reported-by: fuyufan <fuyufan@huawei.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209091928.14766-1-ville.syrjala@linux.intel.comAcked-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/drm_atomic_uapi.c

@@ -76,15 +76,17 @@ int drm_atomic_set_mode_for_crtc(struct drm_crtc_state *state,
 	state->mode_blob = NULL;
 
 	if (mode) {
+		struct drm_property_blob *blob;
+
 		drm_mode_convert_to_umode(&umode, mode);
-		state->mode_blob =
-			drm_property_create_blob(state->crtc->dev,
-						 sizeof(umode),
-						 &umode);
-		if (IS_ERR(state->mode_blob))
-			return PTR_ERR(state->mode_blob);
+		blob = drm_property_create_blob(crtc->dev,
+						sizeof(umode), &umode);
+		if (IS_ERR(blob))
+			return PTR_ERR(blob);
 
 		drm_mode_copy(&state->mode, mode);
+
+		state->mode_blob = blob;
 		state->enable = true;
 		drm_dbg_atomic(crtc->dev,
 			       "Set [MODE:%s] for [CRTC:%d:%s] state %p\n",