ASoC: simple-card: cpu_dai_name creates confusion when DT case

Basically, soc_bind_dai_link() checks
cpu_dai->dev->of_node and dai_link->cpu_of_node in DT case.
But after that it will check
cpu_dai->name and dai_link->cpu_dai_name too.

On the other hand, snd_soc_dai :: name is created by
fmt_single_name() or fmt_multiple_name().

There is no confusion if dai name is created by fmt_multiple_name(),
since cpu_dai->name is same as dai_link->cpu_dai_name.
but, if dai name is created by fmt_single_name(), CPU DAI never match.

Thus, simple-card not set dai_link->cpu_dai_name if DT case
to skip naming match on soc_bind_dai_link()

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