ARM: dts: berlin: Fix schema warnings for pwm-leds

The node names for devices using the pwm-leds driver follow a certain
naming scheme (now).  Parent node name is not enforced, but recommended
by DT project.

  DTC     arch/arm/boot/dts/berlin2cd-google-chromecast.dt.yaml
  CHECK   arch/arm/boot/dts/berlin2cd-google-chromecast.dt.yaml
/home/alex/build/linux/arch/arm/boot/dts/berlin2cd-google-chromecast.dt.yaml: leds: 'red', 'white' do not match any of the regexes: '^led(-[0-9a-f]+)?$', 'pinctrl-[0-9]+'
        From schema: /home/alex/src/linux/leds/Documentation/devicetree/bindings/leds/leds-pwm.yaml

Signed-off-by: Alexander Dahl <post@lespocky.de>
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>