hwmon: (aspeed-pwm-tacho) Switch to using the new API kobj_to_dev()

fixed the following coccicheck:
drivers/hwmon/aspeed-pwm-tacho.c:634:60-61: WARNING opportunity for
kobj_to_dev()
drivers/hwmon/aspeed-pwm-tacho.c:623:60-61: WARNING opportunity for
kobj_to_dev()

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/1609725945-13895-1-git-send-email-tiantao6@hisilicon.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: Tian Tao

drivers/hwmon/aspeed-pwm-tacho.c

@@ -620,7 +620,7 @@ static ssize_t rpm_show(struct device *dev, struct device_attribute *attr,
 static umode_t pwm_is_visible(struct kobject *kobj,
 			      struct attribute *a, int index)
 {
-	struct device *dev = container_of(kobj, struct device, kobj);
+	struct device *dev = kobj_to_dev(kobj);
 	struct aspeed_pwm_tacho_data *priv = dev_get_drvdata(dev);
 
 	if (!priv->pwm_present[index])
@@ -631,7 +631,7 @@ static umode_t pwm_is_visible(struct kobject *kobj,
 static umode_t fan_dev_is_visible(struct kobject *kobj,
 				  struct attribute *a, int index)
 {
-	struct device *dev = container_of(kobj, struct device, kobj);
+	struct device *dev = kobj_to_dev(kobj);
 	struct aspeed_pwm_tacho_data *priv = dev_get_drvdata(dev);
 
 	if (!priv->fan_tach_present[index])