leds: gpio: Use struct_size() in devm_kzalloc()

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes. Also, remove unnecessary
function sizeof_gpio_leds_priv().

This code was detected with the help of Coccinelle and, audited and
fixed manually.
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

drivers/leds/leds-gpio.c

@@ -125,12 +125,6 @@ struct gpio_leds_priv {
 	struct gpio_led_data leds[];
 };
 
-static inline int sizeof_gpio_leds_priv(int num_leds)
-{
-	return sizeof(struct gpio_leds_priv) +
-		(sizeof(struct gpio_led_data) * num_leds);
-}
-
 static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -142,7 +136,7 @@ static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
 	if (!count)
 		return ERR_PTR(-ENODEV);
 
-	priv = devm_kzalloc(dev, sizeof_gpio_leds_priv(count), GFP_KERNEL);
+	priv = devm_kzalloc(dev, struct_size(priv, leds, count), GFP_KERNEL);
 	if (!priv)
 		return ERR_PTR(-ENOMEM);
 
@@ -260,8 +254,7 @@ static int gpio_led_probe(struct platform_device *pdev)
 	int i, ret = 0;
 
 	if (pdata && pdata->num_leds) {
-		priv = devm_kzalloc(&pdev->dev,
-				sizeof_gpio_leds_priv(pdata->num_leds),
+		priv = devm_kzalloc(&pdev->dev, struct_size(priv, leds, pdata->num_leds),
 				    GFP_KERNEL);
 		if (!priv)
 			return -ENOMEM;