ARM: dts: rockchip: Add missing #sound-dai-cells on rk3288

dtc now gives the following warning:

arch/arm/boot/dts/rk3288-tinker.dtb: Warning (sound_dai_property): /sound/simple-audio-card,codec: Missing property '#sound-dai-cells' in node /hdmi@ff980000 or bad phandle (referred from sound-dai[0])

Add the missing #sound-dai-cells property.

Cc: Heiko Stuebner <heiko@sntech.de>
Cc: linux-rockchip@lists.infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>