ALSA: vmaster: Zero-clear ctl before calling slave get

Use kzalloc() instead of kmalloc() so that we don't need to rely fully
on the slave get() callback to clear the control value that might be
copied to user-space.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/vmaster.c

@@ -63,7 +63,7 @@ static int slave_update(struct link_slave *slave)
 	struct snd_ctl_elem_value *uctl;
 	int err, ch;
 
-	uctl = kmalloc(sizeof(*uctl), GFP_KERNEL);
+	uctl = kzalloc(sizeof(*uctl), GFP_KERNEL);
 	if (!uctl)
 		return -ENOMEM;
 	uctl->id = slave->slave.id;