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

Fix W=1 warnings. Two variables are only used for debug logs, mark
with __maybe_unused:

sound/pci/korg1212/korg1212.c: In function ‘snd_korg1212_create’:
sound/pci/korg1212/korg1212.c:2152:36: warning: variable ‘iomem2_size’
set but not used [-Wunused-but-set-variable]
 2152 |  unsigned ioport_size, iomem_size, iomem2_size;
      |                                    ^~~~~~~~~~~
sound/pci/korg1212/korg1212.c:2152:11: warning: variable ‘ioport_size’
set but not used [-Wunused-but-set-variable]
 2152 |  unsigned ioport_size, iomem_size, iomem2_size;
      |           ^~~~~~~~~~~

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200702193604.169059-15-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>