ARM: dts: rockchip: remove clock-frequency from saradc node rv1108

ARM: dts: rockchip: remove clock-frequency from saradc node rv1108

An experimental test with the command below gives these errors:

arch/arm/boot/dts/rv1108-elgin-r1.dt.yaml: adc@1038c000:
'clock-frequency'
does not match any of the regexes: 'pinctrl-[0-9]+'
arch/arm/boot/dts/rv1108-evb.dt.yaml: adc@1038c000:
'clock-frequency'
does not match any of the regexes: 'pinctrl-[0-9]+'

'clock-frequency' is not a valid property for a saradc node,
so remove it.

make ARCH=arm dtbs_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/iio/adc/
rockchip-saradc.yaml

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20200313132646.10317-1-jbx6244@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>