dts/bindings: add '#cells' to nrf-saadc
dts/bindings: add '#cells' to nrf-saadc

This is to support e.g. "<&adc 3>" in the device tree to create e.g.

  DT_FOO_IO_CHANNELS_CONTROLLER = "ADC_0"
  DT_FOO_IO_CHANNELS_INPUT = 3

Signed-off-by: Jim Paris <1cd02e31b43620d7c664e038ca42a060d61727b9@jtan.com>

Vudentz/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr