iio: adc: ad7173: fix calibration channel

iio: adc: ad7173: fix calibration channel

Fix the channel index values passed to ad_sd_calibrate() in
ad7173_calibrate_all().

ad7173_calibrate_all() expects these values to be that of the CHANNELx
register assigned to the channel, not the datasheet INPUTx number of the
channel. The incorrect values were causing register writes to fail for
some channels because they set the WEN bit that must always be 0 for
register access and set the R/W bit to read instead of write. For other
channels, the channel number was just wrong because the CHANNELx
registers are generally assigned in reverse order and so almost never
match the INPUTx numbers.

Fixes: 031bdc8aee01 ("iio: adc: ad7173: add calibration support")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250708-iio-adc-ad7313-fix-calibration-channel-v1-1-e6174e2c7cbf@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>