ASoC: simple-card-utils: add asoc_simple_card_canonicalize_cpu()

simple-card needs remove dai_link->cpu_dai_name if it CPU was
single DAI.
This patch makes this method simple style standard.

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