drm/bridge: ps8640: Return NULL immediately when EDID read fail

drm_edid_read returns NULL on error, so feeding it directly into
drm_edid_duplicate may lead to NULL pointer dereference. Add a check to
guard this.

Fixes: 6a17b4d1 ("drm/bridge: ps8640: Add a cache for EDID")
Signed-off-by: Pin-yen Lin <treapking@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230324035909.1727356-1-treapking@chromium.org

drivers/gpu/drm/bridge/parade-ps8640.c

@@ -543,6 +543,7 @@ static struct edid *ps8640_bridge_get_edid(struct drm_bridge *bridge,
 					   struct drm_connector *connector)
 {
 	struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
+	struct device *dev = &ps_bridge->page[PAGE0_DP_CNTL]->dev;
 	bool poweroff = !ps_bridge->pre_enabled;
 
 	if (!ps_bridge->edid) {
@@ -574,6 +575,11 @@ static struct edid *ps8640_bridge_get_edid(struct drm_bridge *bridge,
 							     connector->state->state);
 	}
 
+	if (!ps_bridge->edid) {
+		dev_err(dev, "Failed to get EDID\n");
+		return NULL;
+	}
+
 	return drm_edid_duplicate(ps_bridge->edid);
 }