ASoC: max9759: fix underflow in speaker_gain_control_put()

Check for negative values of "priv->gain" to prevent an out of bounds
access.  The concern is that these might come from the user via:
  -> snd_ctl_elem_write_user()
    -> snd_ctl_elem_write()
      -> kctl->put()

Fixes: fa8d915 ("ASoC: max9759: Add Amplifier Driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220119123101.GA9509@kili
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/max9759.c

@@ -64,7 +64,8 @@ static int speaker_gain_control_put(struct snd_kcontrol *kcontrol,
 	struct snd_soc_component *c = snd_soc_kcontrol_component(kcontrol);
 	struct max9759 *priv = snd_soc_component_get_drvdata(c);
 
-	if (ucontrol->value.integer.value[0] > 3)
+	if (ucontrol->value.integer.value[0] < 0 ||
+	    ucontrol->value.integer.value[0] > 3)
 		return -EINVAL;
 
 	priv->gain = ucontrol->value.integer.value[0];