ALSA: usb - Fix compile error with CONFIG_SND_DEBUG_VERBOSE=y

Replaced the forgotten cval->mixer->ctrlif.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 035a77b..c166db0 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -306,7 +306,7 @@
 		}
 	}
 	snd_printdd(KERN_ERR "cannot get ctl value: req = %#x, wValue = %#x, wIndex = %#x, type = %d\n",
-		    request, validx, cval->mixer->ctrlif | (cval->id << 8), cval->val_type);
+		    request, validx, snd_usb_ctrl_intf(chip) | (cval->id << 8), cval->val_type);
 	return -EINVAL;
 }