mfd: max8925: fix dt code for backlight

The device-tree enablement for max8925 has several problems, but besides
the bindings being wrong (and not having seen review) there's also some
bad coding practices on how to fill in the platform_data from device tree.

I came across this since it causes a warning when compiling
mmp2_defconfig, and instead of doing the minimal fix to silence the
warning, I restructured the code a bit.

This silences the warning:
drivers/video/backlight/max8925_bl.c: In function 'max8925_backlight_probe':
drivers/video/backlight/max8925_bl.c:177:3: warning: statement with no effect [-Wunused-value]

Note that the bindings themselves need to be revisited too, but that will
affect more than just the backlight driver and is best done separately;
this just fixes the bad code for the backlight driver.

Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

drivers/video/backlight/max8925_bl.c

@@ -101,33 +101,37 @@ static const struct backlight_ops max8925_backlight_ops = {
 	.get_brightness	= max8925_backlight_get_brightness,
 };
 
-#ifdef CONFIG_OF
-static int max8925_backlight_dt_init(struct platform_device *pdev,
-			      struct max8925_backlight_pdata *pdata)
+static void max8925_backlight_dt_init(struct platform_device *pdev)
 {
 	struct device_node *nproot = pdev->dev.parent->of_node, *np;
-	int dual_string;
+	struct max8925_backlight_pdata *pdata;
+	u32 val;
+
+	if (!nproot || !IS_ENABLED(CONFIG_OF))
+		return;
+
+	pdata = devm_kzalloc(&pdev->dev,
+			     sizeof(struct max8925_backlight_pdata),
+			     GFP_KERNEL);
+	if (!pdata)
+		return;
 
-	if (!nproot)
-		return -ENODEV;
 	np = of_find_node_by_name(nproot, "backlight");
 	if (!np) {
 		dev_err(&pdev->dev, "failed to find backlight node\n");
-		return -ENODEV;
+		return;
 	}
 
-	of_property_read_u32(np, "maxim,max8925-dual-string", &dual_string);
-	pdata->dual_string = dual_string;
-	return 0;
+	if (!of_property_read_u32(np, "maxim,max8925-dual-string", &val))
+		pdata->dual_string = val;
+
+	pdev->dev.platform_data = pdata;
 }
-#else
-#define max8925_backlight_dt_init(x, y)	(-1)
-#endif
 
 static int max8925_backlight_probe(struct platform_device *pdev)
 {
 	struct max8925_chip *chip = dev_get_drvdata(pdev->dev.parent);
-	struct max8925_backlight_pdata *pdata = pdev->dev.platform_data;
+	struct max8925_backlight_pdata *pdata;
 	struct max8925_backlight_data *data;
 	struct backlight_device *bl;
 	struct backlight_properties props;
@@ -170,13 +174,10 @@ static int max8925_backlight_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, bl);
 
 	value = 0;
-	if (pdev->dev.parent->of_node && !pdata) {
-		pdata = devm_kzalloc(&pdev->dev,
-				     sizeof(struct max8925_backlight_pdata),
-				     GFP_KERNEL);
-		max8925_backlight_dt_init(pdev, pdata);
-	}
+	if (!pdev->dev.platform_data)
+		max8925_backlight_dt_init(pdev);
 
+	pdata = pdev->dev.platform_data;
 	if (pdata) {
 		if (pdata->lxw_scl)
 			value |= (1 << 7);