ALSA: hda - Fix a unused variable warning

Just overlooked.

sound/pci/hda/patch_realtek.c: In function ‘alc_sku_unsol_event’:
sound/pci/hda/patch_realtek.c:643:19: warning: unused variable ‘spec’ [-Wunused-variable]

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