ALSA: pci/es1938: remove 'set but not used' warning

Fix W=1 warning. Mark the 'audiostatus' variable as __always_unused.

sound/pci/es1938.c: In function ‘snd_es1938_interrupt’:
sound/pci/es1938.c:1622:24: warning: variable ‘audiostatus’ set but
not used [-Wunused-but-set-variable]
 1622 |  unsigned char status, audiostatus;
      |                        ^~~~~~~~~~~

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200702193604.169059-19-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>