iio: adc: ad7380: add ad7389-4

Add chip info for AD7389-4 to the ad7380 driver.

This is essentially the same as ad7380-4 except that it is internal-
reference-only instead of external-reference-only.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250401-iio-ad7380-add-ad7389-4-v1-4-23d2568aa24f@baylibre.com


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