[ALSA] fix selector unit bug affecting some USB speakerphones

Following the suggestion in this thread:
https://bugs.launchpad.net/ubuntu/+source/alsa-lib/+bug/26683
the correct upper bound on desc[0] is 5 + num_ins not 6 + num_ins,
because the index used later is 5+i, not 6+i.
This change makes my Vosky Chatterbox speakerphone work.
Apparently it also helps with the Minivox MV100.
Signed-off-by: Russ Cox <rsc@swtch.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/usb/usbmixer.c

@@ -1483,7 +1483,7 @@ static int parse_audio_selector_unit(struct mixer_build *state, int unitid, unsi
 	struct snd_kcontrol *kctl;
 	char **namelist;
 
-	if (! num_ins || desc[0] < 6 + num_ins) {
+	if (! num_ins || desc[0] < 5 + num_ins) {
 		snd_printk(KERN_ERR "invalid SELECTOR UNIT descriptor %d\n", unitid);
 		return -EINVAL;
 	}