ALSA: azt3328: use proper private_data hookup for codec identification

- much improved implementation due to clean codec hierarchy
- preparation for potential per-codec spinlock change

NOTE: additionally removes a chip->pcm[codec_type] NULL ptr check
(due to it requiring access to external chip struct),
however I believe this to be ok since this condition should not occur
and most drivers don't check against that either.
Signed-off-by: Andreas Mohr <andi@lisas.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>