ALSA: oxygen: Fix logical-not-parentheses warning

This fixes the following warning, that is seen with gcc 5.1:
warning: logical not is only applied to the left hand side of comparison [-Wlogical-not-parentheses].
Signed-off-by: NTomer Barletz <barletz@gmail.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/oxygen/oxygen_mixer.c

@@ -88,7 +88,7 @@ static int dac_mute_put(struct snd_kcontrol *ctl,
 	int changed;
 
 	mutex_lock(&chip->mutex);
-	changed = !value->value.integer.value[0] != chip->dac_mute;
+	changed = (!value->value.integer.value[0]) != chip->dac_mute;
 	if (changed) {
 		chip->dac_mute = !value->value.integer.value[0];
 		chip->model.update_dac_mute(chip);