ALSA: scarlett2: Add clamp() in scarlett2_mixer_ctl_put()

Ensure the value passed to scarlett2_mixer_ctl_put() is between 0 and
SCARLETT2_MIXER_MAX_VALUE so we don't attempt to access outside
scarlett2_mixer_values[].
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Fixes: 9e4d5c1b ("ALSA: usb-audio: Scarlett Gen 2 mixer interface")
Link: https://lore.kernel.org/r/3b19fb3da641b587749b85fe1daa1b4e696c0c1b.1703001053.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett2.c

@@ -3663,7 +3663,8 @@ static int scarlett2_mixer_ctl_put(struct snd_kcontrol *kctl,
 	mutex_lock(&private->data_mutex);
 
 	oval = private->mix[index];
-	val = ucontrol->value.integer.value[0];
+	val = clamp(ucontrol->value.integer.value[0],
+		    0L, (long)SCARLETT2_MIXER_MAX_VALUE);
 	num_mixer_in = port_count[SCARLETT2_PORT_TYPE_MIX][SCARLETT2_PORT_OUT];
 	mix_num = index / num_mixer_in;