dt-bindings: iio: adc: Add rockchip,rk3588-saradc string

Add rockchip,rk3588-saradc compatible string.

Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230603185340.13838-9-shreeya.patel@collabora.com


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