ALSA: scarlett2: Correct channel mute status after mute button pressed

After the hardware mute button is pressed, private->vol_updated is set
so that the mute status is invalidated. As the channel mute values may
be affected by the global mute value, update scarlett2_mute_ctl_get()
to call scarlett2_update_volumes() if private->vol_updated is set.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/aa18ddbf8d8bd7f31832ab1b6b6057c00b931202.1626959758.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -1856,9 +1856,15 @@ static int scarlett2_mute_ctl_get(struct snd_kcontrol *kctl,
 					struct snd_ctl_elem_value *ucontrol)
 {
 	struct usb_mixer_elem_info *elem = kctl->private_data;
-	struct scarlett2_data *private = elem->head.mixer->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_data *private = mixer->private_data;
 	int index = line_out_remap(private, elem->control);
 
+	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
+		scarlett2_update_volumes(mixer);
+	mutex_unlock(&private->data_mutex);
+
 	ucontrol->value.integer.value[0] = private->mute_switch[index];
 	return 0;
 }