ASoC: hdac_hdmi: keep DAI driver pointer in private data

struct snd_soc_component::dai_drv will be removed soon.
hdac_hdmi is only user of it. Let's keep it on private data.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>