iio: Add ABI documentation for in_magn offset value

This patch adds ABI documentation entries for in_magn_offset.
There is one user, hid-sensor-magn-3d in drivers/iio/magnetometer.

Signed-off-by: Darshana Padmadas <[email protected]>
Reviewed-by: Daniel Baluta <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>

Author: darshanapdas

Documentation/ABI/testing/sysfs-bus-iio

@@ -253,6 +253,7 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_temp_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressureY_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressure_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_humidityrelative_offset
+What:		/sys/bus/iio/devices/iio:deviceX/in_magn_offset
 KernelVersion:	2.6.35
 Contact:	[email protected]
 Description: