ASoC: switch over to use snd_soc_register_component() on sh4 siu

siu_dai.c is using snd_soc_register_dais(),
even though array size of siu_i2s_dai is 1.
OTOH, new API snd_soc_register_component() uses properly
snd_soc_register_dai()  (henceforth dai()) or
snd_soc_register_dais() (henceforth dais()) via num_dai.
Then, cpu_dai_name will be "siu-i2s-dai" if dais() was used,
and it will be "siu-pcm-audio" if dai() was used.
Therefore this patch fixup migor_dai :: cpu_dai_name too.

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