dt-bindings: iio: rockchip: Fix 'oneOf' condition failed warning

rk3588-saradc isn't compatible with the rk3399-saradc variant,
hence, fix the following dtbs_check warning for 'oneOf' condition
failure.

DTC_CHK arch/arm64/boot/dts/rockchip/rk3588-rock-5b.dtb
/home/shreeya/linux/arch/arm64/boot/dts/rockchip/rk3588-rock-5b.dtb:
	saradc@fec10000: compatible: 'oneOf' conditional failed,
	one must be fixed:
	['rockchip,rk3588-saradc'] is too short
	'rockchip,saradc' was expected
	'rockchip,rk3066-tsadc' was expected
	'rockchip,rk3399-saradc' was expected

Fixes: 2daf2ae9 ("dt-bindings: iio: adc: Add rockchip,rk3588-saradc string")
Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230610143601.173307-1-shreeya.patel@collabora.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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

@@ -15,13 +15,13 @@ properties:
       - const: rockchip,saradc
       - const: rockchip,rk3066-tsadc
       - const: rockchip,rk3399-saradc
+      - const: rockchip,rk3588-saradc
       - items:
           - enum:
               - rockchip,px30-saradc
               - rockchip,rk3308-saradc
               - rockchip,rk3328-saradc
               - rockchip,rk3568-saradc
-              - rockchip,rk3588-saradc
               - rockchip,rv1108-saradc
               - rockchip,rv1126-saradc
           - const: rockchip,rk3399-saradc