This patch solve compile error when .config doesn't have
CONFIG_SND_SOC which is needed for HDMI sound.
It was reported by Guennadi as follows

Besides, I think, this will not link without CONFIG_SND_SOC.
Reported-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: NLiam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>