Staging: iio: max1363 Fix two bugs in single_channel_from_ring

This patch contains fixes for the two bugs Michael pointed
out last week.  As the other suggestion Michael made is
not a bug fix (just a much more sensible way of handling
things), I'll do that as a separate patch soon.

The bugs were introduced with the abi changes.

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