[ALSA] usb audio: Fix another Dallas quirk

Dallas USB speakers are buggy in more than one way. One of configs
they offer does not work at all.
Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/usbaudio.c

@@ -2676,12 +2676,23 @@ static int parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
 	int format;
 	struct audioformat *fp;
 	unsigned char *fmt, *csep;
+	int num;
 
 	dev = chip->dev;
 
 	/* parse the interface's altsettings */
 	iface = usb_ifnum_to_if(dev, iface_no);
-	for (i = 0; i < iface->num_altsetting; i++) {
+
+	num = iface->num_altsetting;
+
+	/*
+	 * Dallas DS4201 workaround: It presents 5 altsettings, but the last
+	 * one misses syncpipe, and does not produce any sound.
+	 */
+	if (chip->usb_id == USB_ID(0x04fa, 0x4201))
+		num = 4;
+
+	for (i = 0; i < num; i++) {
 		alts = &iface->altsetting[i];
 		altsd = get_iface_desc(alts);
 		/* skip invalid one */