dt-bindings: iio: rockchip-saradc: add support for rk3328

The rk3328 saradc is the same as rk3399.
Signed-off-by: NLiang Chen <cl@rock-chips.com>
Reviewed-by: NHeiko Stuebner <heiko@sntech.de>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/rockchip-saradc.txt

@@ -4,6 +4,7 @@ Required properties:
 - compatible: should be "rockchip,<name>-saradc" or "rockchip,rk3066-tsadc"
    - "rockchip,saradc": for rk3188, rk3288
    - "rockchip,rk3066-tsadc": for rk3036
+   - "rockchip,rk3328-saradc", "rockchip,rk3399-saradc": for rk3328
    - "rockchip,rk3399-saradc": for rk3399
 
 - reg: physical base address of the controller and length of memory mapped