ALSA: pci/via82xx: remove 'set but not used' warnings

Fix W=1 warnings. Mark variables as __always_unused.

sound/pci/via82xx.c: In function ‘snd_via82xx_codec_wait’:
sound/pci/via82xx.c:547:6: warning: variable ‘err’ set but not used
[-Wunused-but-set-variable]
  547 |  int err;
      |      ^~~
sound/pci/via82xx_modem.c: In function ‘snd_via82xx_codec_wait’:
sound/pci/via82xx_modem.c:401:6: warning: variable ‘err’ set but not
used [-Wunused-but-set-variable]
  401 |  int err;
      |      ^~~

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200702193604.169059-21-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>