ASoC: wm2200: use snd_soc_codec_get_drvdata()

snd_soc_codec_get_drvdata() is common function to get
private data. Let's use it.

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