hwmon: (i5k_amb) fix checkpatch issues

fixed:
WARNING: simple_strtoul is obsolete, use kstrtoul instead
+	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;

WARNING: simple_strtoul is obsolete, use kstrtoul instead
+	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;

WARNING: simple_strtoul is obsolete, use kstrtoul instead
+	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Acked-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

drivers/hwmon/i5k_amb.c

@@ -159,8 +159,12 @@ static ssize_t store_amb_min(struct device *dev,
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
 	struct i5k_amb_data *data = dev_get_drvdata(dev);
-	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;
+	unsigned long temp;
+	int ret = kstrtoul(buf, 10, &temp);
+	if (ret < 0)
+		return ret;
 
+	temp = temp / 500;
 	if (temp > 255)
 		temp = 255;
 
@@ -175,8 +179,12 @@ static ssize_t store_amb_mid(struct device *dev,
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
 	struct i5k_amb_data *data = dev_get_drvdata(dev);
-	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;
+	unsigned long temp;
+	int ret = kstrtoul(buf, 10, &temp);
+	if (ret < 0)
+		return ret;
 
+	temp = temp / 500;
 	if (temp > 255)
 		temp = 255;
 
@@ -191,8 +199,12 @@ static ssize_t store_amb_max(struct device *dev,
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
 	struct i5k_amb_data *data = dev_get_drvdata(dev);
-	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;
+	unsigned long temp;
+	int ret = kstrtoul(buf, 10, &temp);
+	if (ret < 0)
+		return ret;
 
+	temp = temp / 500;
 	if (temp > 255)
 		temp = 255;