drm/rockchip: cdn-dp-core: add missing clk_disable_unprepare() on error in cdn_dp_grf_write()

After calling clk_prepare_enable(), clk_disable_unprepare() need
be called when calling regmap_write() failed.

Fixes: 1a0f7ed3 ("drm/rockchip: cdn-dp: add cdn DP support for rk3399")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210519134928.2696617-1-yangyingliang@huawei.com

drivers/gpu/drm/rockchip/cdn-dp-core.c

@@ -73,6 +73,7 @@ static int cdn_dp_grf_write(struct cdn_dp_device *dp,
 	ret = regmap_write(dp->grf, reg, val);
 	if (ret) {
 		DRM_DEV_ERROR(dp->dev, "Could not write to GRF: %d\n", ret);
+		clk_disable_unprepare(dp->grf_clk);
 		return ret;
 	}