iio: adc: ad7173: don't make copy of ad_sigma_delta_info struct

Use two separate static const struct ad_sigma_delta_info instances
instead of making a copy for each driver instance.

Typically in the IIO subsystem, we use multiple static const instances
of the same struct when there are different variants of the same family
of devices as opposed to making a copy for each driver instance and
modifying it.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250113-iio-adc-ad7313-fix-non-const-info-struct-v4-2-b63be3ecac4a@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>