ALSA: usb-audio: store protocol version in struct audioformat

Instead of reading bInterfaceProtocol from the descriptor whenever it's
needed, store this value in the audioformat structure.  Besides
simplifying some code, this will allow us to correctly handle vendor-
specific devices where the descriptors are marked with other values.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

sound/usb/pcm.c

@@ -202,13 +202,11 @@ int snd_usb_init_pitch(struct snd_usb_audio *chip, int iface,
 		       struct usb_host_interface *alts,
 		       struct audioformat *fmt)
 {
-	struct usb_interface_descriptor *altsd = get_iface_desc(alts);
-
 	/* if endpoint doesn't have pitch control, bail out */
 	if (!(fmt->attributes & UAC_EP_CS_ATTR_PITCH_CONTROL))
 		return 0;
 
-	switch (altsd->bInterfaceProtocol) {
+	switch (fmt->protocol) {
 	case UAC_VERSION_1:
 	default:
 		return init_pitch_v1(chip, iface, alts, fmt);