ALSA: ak411x: Fix race of reinit() calls

Protect the call with a mutex, as this may be called in parallel
(either from the PCM rate change and the clock change).

Acked-by: Jaroslav Kysela <perex@perex.cz>
Tested-by: Pavel Hofman <pavel.hofman@ivitera.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>