staging:iio: ad7152: fix channel assignment for AD7153

In case the AD7153 is selected we need to make sure we provide channel info
for the first capacitance input in both single ended and differential
configuration.

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