ASoC: adau1372: fix mclk

ASoC: adau1372: fix mclk

"mclk" is retrieved from the configuration and assigned to adau1372->clk.
However adau1372->mclk (==NULL) is used for clk_prepare_enable() and
clk_disable_unprepare() which don't have any effect.

Remove .clk from struct adau1372 and use .mclk throughout.
This change ensures that the input clock is switched on/off when the
bias level is changed.

Signed-off-by: Maarten Zanders <maarten.zanders@mind.be>
Link: https://lore.kernel.org/r/20221028152626.109603-2-maarten.zanders@mind.be
Signed-off-by: Mark Brown <broonie@kernel.org>