hwmon: (nct6775) Only display fan speed tolerance conditionally

 * Fan speed tolerance is a tricky beast, since the associated register is

 * a tick counter, but the value is reported and configured as rpm.

 * Compute resulting low and high rpm values and report the difference.

 * A fan speed tolerance only makes sense if a fan target speed has been

 * configured, so only display values other than 0 if that is the case.

 */

static ssize_t

show_speed_tolerance(struct device *dev, struct device_attribute *attr,

	struct nct6775_data *data = nct6775_update_device(dev);

	struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);

	int nr = sattr->index;

	int low = data->target_speed[nr] - data->target_speed_tolerance[nr];

	int high = data->target_speed[nr] + data->target_speed_tolerance[nr];

	int tolerance;

	int target = data->target_speed[nr];

	int tolerance = 0;

	if (target) {

		int low = target - data->target_speed_tolerance[nr];

		int high = target + data->target_speed_tolerance[nr];

		if (low <= 0)

			low = 1;

		tolerance = (fan_from_reg16(low, data->fan_div[nr])

			     - fan_from_reg16(high, data->fan_div[nr])) / 2;

	}

	return sprintf(buf, "%d\n", tolerance);

}