ALSA: hda - Fix an "unused variable" compile warning

Forgot to remove an unused variable.
  sound/pci/hda/patch_realtek.c: In function ‘alc882_auto_init_analog_input’:
  sound/pci/hda/patch_realtek.c:7018: warning: unused variable ‘vref’
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_realtek.c

@@ -7015,7 +7015,6 @@ static void alc882_auto_init_analog_input(struct hda_codec *codec)
 
 	for (i = 0; i < AUTO_PIN_LAST; i++) {
 		hda_nid_t nid = spec->autocfg.input_pins[i];
-		unsigned int vref;
 		if (!nid)
 			continue;
 		alc_set_input_pin(codec, nid, AUTO_PIN_FRONT_MIC /*i*/);