These bindings !include adc.yaml, but their device tree nodes never set
'clocks':
dts/bindings/iio/adc/atmel,sam-afec.yaml
dts/bindings/iio/adc/atmel,sam0-adc.yaml
dts/bindings/iio/adc/nordic,nrf-adc.yaml
dts/bindings/iio/adc/nordic,nrf-saadc.yaml
The nodes for these bindings do set it (think it's consistent for
st,stm32-adc.yaml):
dts/bindings/iio/adc/nxp,kinetis-adc12.yaml
dts/bindings/iio/adc/st,stm32-adc.yaml
Make 'clocks' optional in adc.yaml. Maybe it should be changed to
required on some platforms (!including bindings can change 'optional' to
'required').
Fixes a bunch of errors in
https://github.com/zephyrproject-rtos/zephyr/issues/17532.
Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>
c023495df0