iio: adc: ad7124: fix channel lookup in syscalib functions

iio: adc: ad7124: fix channel lookup in syscalib functions

Fix possible incorrect channel lookup in the syscalib functions by using
the correct channel address instead of the channel number.

In the ad7124 driver, the channel field of struct iio_chan_spec is the
input pin number of the positive input of the channel. This can be, but
is not always the same as the index in the channels array. The correct
index in the channels array is stored in the address field (and also
scan_index). We use the address field to perform the correct lookup.

Fixes: 47036a03a303 ("iio: adc: ad7124: Implement internal calibration at probe time")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250726-iio-adc-ad7124-fix-channel-lookup-in-syscalib-v1-1-b9d14bb684af@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>