PM / devfreq: rockchip-dfi: Make pmu regmap mandatory

As a matter of fact the regmap_pmu already is mandatory because
it is used unconditionally in the driver. Bail out gracefully in
probe() rather than crashing later.

Link: https://lore.kernel.org/lkml/20230704093242.583575-2-s.hauer@pengutronix.de/
Fixes: b9d1262b ("PM / devfreq: event: support rockchip dfi controller")
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/devfreq/event/rockchip-dfi.c

@@ -193,14 +193,15 @@ static int rockchip_dfi_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(data->clk),
 				     "Cannot get the clk pclk_ddr_mon\n");
 
-	/* try to find the optional reference to the pmu syscon */
 	node = of_parse_phandle(np, "rockchip,pmu", 0);
-	if (node) {
-		data->regmap_pmu = syscon_node_to_regmap(node);
-		of_node_put(node);
-		if (IS_ERR(data->regmap_pmu))
-			return PTR_ERR(data->regmap_pmu);
-	}
+	if (!node)
+		return dev_err_probe(&pdev->dev, -ENODEV, "Can't find pmu_grf registers\n");
+
+	data->regmap_pmu = syscon_node_to_regmap(node);
+	of_node_put(node);
+	if (IS_ERR(data->regmap_pmu))
+		return PTR_ERR(data->regmap_pmu);
+
 	data->dev = dev;
 
 	desc = devm_kzalloc(dev, sizeof(*desc), GFP_KERNEL);