staging:iio:gyro:adis16080 convert to iio_chan_spec.

This is a rare driver that is so simple it actually gets longer
as a result of this conversion.  Oh well, swings and roundabouts.

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>