ALSA: pci/korg1212: completely remove 'set but not used' warnings

Commit 6cdc01eb ("ALSA: pci/korg1212: remove 'set but not used'
warnings") missed one __maybe_unused, add to enable make W=1 sound/
compilation with x86_64 allmodconfig

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210804185442.274057-1-pierre-louis.bossart@linux.intel.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>