ASoC: ak4642: Replace mdelay function to msleep

Replace mdelay to msleep to avoid busy loop on ak4642_lout_event().
Otherwise, sometimes playback doesn't work correctly when pulseaudio
was used.

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