drm/panel: fix a possible null pointer dereference

In versatile_panel_get_modes(), the return value of drm_mode_duplicate()
is assigned to mode, which will lead to a NULL pointer dereference
on failure of drm_mode_duplicate(). Add a check to avoid npd.
Signed-off-by: Ma Ke <make_ruc2021@163.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20231007033105.3997998-1-make_ruc2021@163.comSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231007033105.3997998-1-make_ruc2021@163.com

drivers/gpu/drm/panel/panel-arm-versatile.c

@@ -267,6 +267,8 @@ static int versatile_panel_get_modes(struct drm_panel *panel,
 	connector->display_info.bus_flags = vpanel->panel_type->bus_flags;
 
 	mode = drm_mode_duplicate(connector->dev, &vpanel->panel_type->mode);
+	if (!mode)
+		return -ENOMEM;
 	drm_mode_set_name(mode);
 	mode->type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;