drm/mediatek: Remove the unneeded result

Return the value drm_mode_config_helper_suspend() directly instead of
 storing it in another redundant variable.
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220825072335.228921-1-ye.xingchen@zte.com.cn/Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/mtk_drm_drv.c

@@ -833,11 +833,8 @@ static int mtk_drm_sys_prepare(struct device *dev)
 {
 	struct mtk_drm_private *private = dev_get_drvdata(dev);
 	struct drm_device *drm = private->drm;
-	int ret;
-
-	ret = drm_mode_config_helper_suspend(drm);
 
-	return ret;
+	return drm_mode_config_helper_suspend(drm);
 }
 
 static void mtk_drm_sys_complete(struct device *dev)