iio: adc: rockchip_saradc: Use of_device_get_match_data

Use of_device_get_match_data() to simplify the code.

Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20230603185340.13838-5-shreeya.patel@collabora.com


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