ALSA: snd-usb: use ep->stride from urb callbacks

For normal PCM transfer, this change has no effect, as the endpoint's
stride is always frame_bits/8. For DSD DOP streams, however, which is
added later, the hardware stride differs from the software stride, and
the endpoint has the correct information in these cases.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/pcm.c

@@ -1236,8 +1236,8 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 			counts = snd_usb_endpoint_next_packet_size(ep);
 
 		/* set up descriptor */
-		urb->iso_frame_desc[i].offset = frames * stride;
-		urb->iso_frame_desc[i].length = counts * stride;
+		urb->iso_frame_desc[i].offset = frames * ep->stride;
+		urb->iso_frame_desc[i].length = counts * ep->stride;
 		frames += counts;
 		urb->number_of_packets++;
 		subs->transfer_done += counts;
@@ -1251,14 +1251,14 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 					frames -= subs->transfer_done;
 					counts -= subs->transfer_done;
 					urb->iso_frame_desc[i].length =
-						counts * stride;
+						counts * ep->stride;
 					subs->transfer_done = 0;
 				}
 				i++;
 				if (i < ctx->packets) {
 					/* add a transfer delimiter */
 					urb->iso_frame_desc[i].offset =
-						frames * stride;
+						frames * ep->stride;
 					urb->iso_frame_desc[i].length = 0;
 					urb->number_of_packets++;
 				}
@@ -1269,7 +1269,7 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 		    !snd_usb_endpoint_implicit_feedback_sink(subs->data_endpoint)) /* finish at the period boundary */
 			break;
 	}
-	bytes = frames * stride;
+	bytes = frames * ep->stride;
 	if (subs->hwptr_done + bytes > runtime->buffer_size * stride) {
 		/* err, the transferred area goes over buffer boundary. */
 		unsigned int bytes1 =
@@ -1310,8 +1310,8 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
 {
 	unsigned long flags;
 	struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
-	int stride = runtime->frame_bits >> 3;
-	int processed = urb->transfer_buffer_length / stride;
+	struct snd_usb_endpoint *ep = subs->data_endpoint;
+	int processed = urb->transfer_buffer_length / ep->stride;
 	int est_delay;
 
 	/* ignore the delay accounting when procssed=0 is given, i.e.