iio: hid-sensors: Move get sensitivity attribute to hid-sensor-common

iio: hid-sensors: Move get sensitivity attribute to hid-sensor-common

No functional change has been made with this patch. The main intent here
is to reduce code repetition of getting sensitivity attribute.

In the current implementation, sensor_hub_input_get_attribute_info() is
called from multiple drivers to get attribute info for sensitivity
field. Moving this to common place will avoid code repetition.

Signed-off-by: Ye Xiang <xiang.ye@intel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210201054921.18214-2-xiang.ye@intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>