ASoC: soc-pcm: add snd_soc_dai_get_widget()

soc-pcm.c has dai_get_widget(), but it can be more generic.
This patch renames it to snd_soc_dai_get_widget(), and use it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87d0abjca1.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>