[ALSA] ak4114 - Fix possible Oops with callbacks

ak4114 code may trigger Oops when the parameters are changed without
call of snd_ak4114_build().  Now it checks the existence of kctl
element, and the workq is triggered after building the necessary
kcontrols.
Also, did some code clean up.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>