sound: control: fix minimum TLV length

Allow TLV blocks that do not have any values; the smallest possible TLV
is an empty container or one where the information is only in the tag.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

sound/core/control.c

@@ -1100,7 +1100,7 @@ static int snd_ctl_tlv_ioctl(struct snd_ctl_file *file,
 
 	if (copy_from_user(&tlv, _tlv, sizeof(tlv)))
 		return -EFAULT;
-	if (tlv.length < sizeof(unsigned int) * 3)
+	if (tlv.length < sizeof(unsigned int) * 2)
 		return -EINVAL;
 	down_read(&card->controls_rwsem);
 	kctl = snd_ctl_find_numid(card, tlv.numid);