ALSA: usb-audio: scarlett2: Add temp variable for consistency

Add index temporary variable to scarlett2_mixer_ctl_put() for
consistency with the other *_ctl_put() functions.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/20210620164641.GA9211@m.b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -1622,18 +1622,19 @@ static int scarlett2_mixer_ctl_put(struct snd_kcontrol *kctl,
 	const struct scarlett2_device_info *info = private->info;
 	const struct scarlett2_ports *ports = info->ports;
 	int oval, val, num_mixer_in, mix_num, err = 0;
+	int index = elem->control;
 
 	mutex_lock(&private->data_mutex);
 
-	oval = private->mix[elem->control];
+	oval = private->mix[index];
 	val = ucontrol->value.integer.value[0];
 	num_mixer_in = ports[SCARLETT2_PORT_TYPE_MIX].num[SCARLETT2_PORT_OUT];
-	mix_num = elem->control / num_mixer_in;
+	mix_num = index / num_mixer_in;
 
 	if (oval == val)
 		goto unlock;
 
-	private->mix[elem->control] = val;
+	private->mix[index] = val;
 	err = scarlett2_usb_set_mix(mixer, mix_num);
 	if (err == 0)
 		err = 1;