iio: hid-sensor-als: Add relative hysteresis support

Hid sensor als use relative hysteresis, this patch adds the support.

Signed-off-by: Ye Xiang <xiang.ye@intel.com>
Link: https://lore.kernel.org/r/20210207070048.23935-3-xiang.ye@intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>