ASoC: soc-core: remove OF adjusting for snd_soc_of_parse_audio_prefix

Because prototype of OF-graph sound card support didn't have Sound Card
node, commit b6defcca
("ASoC: soc-core: adjust for graph on snd_soc_of_parse_audio_prefix")
adjusted to it on each functions.

But final discussion result of ALSA SoC / OF-graph ML, OF-graph sound
card has node. Thus, this commit became no longer needed.

This reverts commit b6defcca.

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