ASoC: nau8822: Remove unused member from struct

Remove unused mclk_idx struct member.
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://msgid.link/r/20240404111953.99287-1-francesco@dolcini.itSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/nau8822.h

@@ -215,7 +215,6 @@ struct nau8822_pll {
 struct nau8822 {
 	struct device *dev;
 	struct regmap *regmap;
-	int mclk_idx;
 	struct nau8822_pll pll;
 	int sysclk;
 	int div_id;