ARM: Kirkwood: DT: Add missing #sound-dai-cells property

The sound node is missing a #sound-dai-cells property. Add it, so that
the sounds node can be used in combination with the simple-audio-card
binding.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lkml.kernel.org/r/1399141819-23924-5-git-send-email-andrew@lunn.ch


Signed-off-by: Jason Cooper <jason@lakedaemon.net>