dt-bindings: display: add #sound-dai-cells property to rockchip rk3066 hdmi

The Rockchip rk3066 HDMI controller can take one I2S input and transmit it
over the HDMI output. Add #sound-dai-cells (= 0) to the binding for it.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/b9864655-7c60-4066-8305-f291a3551872@gmail.com