ALSA: usb-audio: scarlett2: Fix data_mutex lock

The private->vol_updated flag was being checked outside of the
mutex_lock/unlock() of private->data_mutex leading to the volume data
being fetched twice from the device unnecessarily or old volume data
being returned.

Update scarlett2_*_ctl_get() and include the private->vol_updated flag
check inside the critical region.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/20210620164643.GA9216@m.b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -1153,11 +1153,10 @@ static int scarlett2_master_volume_ctl_get(struct snd_kcontrol *kctl,
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_data *private = mixer->private_data;
 
-	if (private->vol_updated) {
 	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
 		scarlett2_update_volumes(mixer);
 	mutex_unlock(&private->data_mutex);
-	}
 
 	ucontrol->value.integer.value[0] = private->master_vol;
 	return 0;
@@ -1171,11 +1170,10 @@ static int scarlett2_volume_ctl_get(struct snd_kcontrol *kctl,
 	struct scarlett2_data *private = mixer->private_data;
 	int index = elem->control;
 
-	if (private->vol_updated) {
 	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
 		scarlett2_update_volumes(mixer);
 	mutex_unlock(&private->data_mutex);
-	}
 
 	ucontrol->value.integer.value[0] = private->vol[index];
 	return 0;
@@ -1439,11 +1437,10 @@ static int scarlett2_dim_mute_ctl_get(struct snd_kcontrol *kctl,
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_data *private = mixer->private_data;
 
-	if (private->vol_updated) {
 	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
 		scarlett2_update_volumes(mixer);
 	mutex_unlock(&private->data_mutex);
-	}
 
 	ucontrol->value.enumerated.item[0] = private->dim_mute[elem->control];
 	return 0;