iio: hid-sensor-prox: Fix scale not correct issue

Currently, the proxy sensor scale is zero because it just return the
exponent directly. To fix this issue, this patch use
hid_sensor_format_scale to process the scale first then return the
output.

Fixes: 39a3a0138f ("iio: hid-sensors: Added Proximity Sensor Driver")
Signed-off-by: Ye Xiang <xiang.ye@intel.com>
Link: https://lore.kernel.org/r/20210130102530.31064-1-xiang.ye@intel.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/hid-sensor-prox.c

@@ -23,6 +23,9 @@ struct prox_state {
 	struct hid_sensor_common common_attributes;
 	struct hid_sensor_hub_attribute_info prox_attr;
 	u32 human_presence;
+	int scale_pre_decml;
+	int scale_post_decml;
+	int scale_precision;
 };
 
 /* Channel definitions */
@@ -93,8 +96,9 @@ static int prox_read_raw(struct iio_dev *indio_dev,
 		ret_type = IIO_VAL_INT;
 		break;
 	case IIO_CHAN_INFO_SCALE:
-		*val = prox_state->prox_attr.units;
-		ret_type = IIO_VAL_INT;
+		*val = prox_state->scale_pre_decml;
+		*val2 = prox_state->scale_post_decml;
+		ret_type = prox_state->scale_precision;
 		break;
 	case IIO_CHAN_INFO_OFFSET:
 		*val = hid_sensor_convert_exponent(
@@ -234,6 +238,11 @@ static int prox_parse_report(struct platform_device *pdev,
 			HID_USAGE_SENSOR_HUMAN_PRESENCE,
 			&st->common_attributes.sensitivity);
 
+	st->scale_precision = hid_sensor_format_scale(
+				hsdev->usage,
+				&st->prox_attr,
+				&st->scale_pre_decml, &st->scale_post_decml);
+
 	return ret;
 }