Add saradc compatible string for rockchip rv1126.

Cc: linux-iio@vger.kernel.org
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jagan Teki <jagan@edgeble.ai>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221108041400.157052-4-jagan@edgeble.aiSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>