ALSA: usb-audio: Fix the first PCM interface assignment

In the new PCM streaming logic, the interface number is assigned to
usb stream instance (subs->interface) after the format and rate setups
are succeeded, but some codes are still passing subs->interface as the
reference to helper functions. This leads to initializing with an
invalid iface number (-1).

This patch replaces the wrong references with the ones from the target
fmt correctly.

Signed-off-by: Takashi Iwai <[e-mail]>

sound/usb/pcm.c

···
 		subs->data_endpoint->sync_master = subs->sync_endpoint;
 	}
 
-	if ((err = snd_usb_init_pitch(subs->stream->chip, subs->interface, alts, fmt)) < 0)
+	if ((err = snd_usb_init_pitch(subs->stream->chip, fmt->iface, alts, fmt)) < 0)
 		return err;
 
 	subs->cur_audiofmt = fmt;
···
 		struct usb_interface *iface;
 		iface = usb_ifnum_to_if(subs->dev, fmt->iface);
 		alts = &iface->altsetting[fmt->altset_idx];
-		ret = snd_usb_init_sample_rate(subs->stream->chip, subs->interface, alts, fmt, rate);
+		ret = snd_usb_init_sample_rate(subs->stream->chip, fmt->iface, alts, fmt, rate);
 		if (ret < 0)
 			return ret;
 		subs->cur_rate = rate;