staging: iio: ad7192: Fix ad7193 channel address

commit 7ce0f216 upstream.

This patch fixes the differential channels addresses for the ad7193.

Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>