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

The Rockchip inno 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/521d4229-7490-4494-8191-cd5f3119249e@gmail.com