ALSA: usb-audio: Downgrade error message in get_ctl_value_v2()

The error message in get_ctl_value_v2() (for UAC2/3) is shown via
KERN_ERR level but it was intended to be rather a debug message as
seen in get_ctl_value_v1() (for UAC1).  This patch downgrade the
printk level.
Tested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20211014130636.17860-2-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -373,7 +373,7 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 
 	if (ret < 0) {
 error:
-		usb_audio_err(chip,
+		usb_audio_dbg(chip,
 			"cannot get ctl value: req = %#x, wValue = %#x, wIndex = %#x, type = %d\n",
 			request, validx, idx, cval->val_type);
 		return ret;