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

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: 39a3a0138f61 ("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>