staging:iio:gyro:adis16130 drop control of adc resolution.

There is no clear use case for this functionality in a driver
that only supports slow reading via sysfs. The interface
use was non compliant with the abi motiving it being dropped.

It can go back in if anyone ever implements buffered reading
support for this device.  Then it will be controlled as
part of the buffering abi where this should indeed be correctly
supported.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>