staging:iio:adc: max1363 fix 2 raw sysfs issues.

indio_dev->channels was accidentally removed thus preventing any sysfs
registrations occuring for direct reading.  That hid the other issue.

Unfortunately the incorrect handling leads to misspresentation of data
in sysfs reads.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>