ALSA: PCI168 snd-azt3328: some more fixups

- fix problem with codec register 0x6a being write-only
  by adding a software shadow register
  (caused annoying noise after module loading due to _toggling_
  between gameport and audio bits instead of configuring them properly)
- rename several "Wave" mixer controls to "PCM", since this is
  what Wine and several other apps are looking for (IOW, _requiring_)
  and this is what AC97 specs use as naming, too,
  thus I'd guess it's what these controls are
- cleanup, small optimizations

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