staging:iio:light:isl29018: Convert some of the isl29018 driver to the new iio_chan_spec framework.

Remove the driver's get_sensor_data() interfaces and replace them with
iio_chan_spec channels.  This converts 4 files to the new framework.
Driver ABI change: The intensity_infrared_raw file is now intensity_ir_raw.

Signed-off-by: Bryan Freed <bfreed@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>