iio: adc: mt6359: Add ready register index and mask to channel data

iio: adc: mt6359: Add ready register index and mask to channel data

In preparation for adding support for the AUXADC block found in
the MT6363 PMIC, add the ready register index and mask to the
mtk_pmic_auxadc_chan structure, populate those in the channel
description for all of the already supported SoCs and make use
of them in the .read_imp() callbacks.

Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250703141146.171431-4-angelogioacchino.delregno@collabora.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>