staging: line6: fix playback urb transfer buffer calculation

The playback urb transfer buffer calculation does not factor in
LINE6_ISO_PACKETS.  Buffer memory is organized like this in the driver:

  Buffer 0                 Buffer 1                 ...
  [Packet 0, Packet 1, ...][Packet 0, Packet 1, ...][Packet 0, ...]

However, we're lucky that LINE6_ISO_PACKETS is currently defined as 1 so
this patch does not change any behavior.  It's still worth including
this fix in case the LINE6_ISO_PACKETS value is changed in the future.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Markus Grabner <grabner@icg.tugraz.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/line6/playback.c

@@ -192,7 +192,7 @@ static int submit_audio_out_urb(struct snd_line6_pcm *line6pcm)
 	urb_frames = urb_size / bytes_per_frame;
 	urb_out->transfer_buffer =
 	    line6pcm->buffer_out +
-	    line6pcm->max_packet_size * line6pcm->index_out;
+	    LINE6_ISO_PACKETS * line6pcm->max_packet_size * line6pcm->index_out;
 	urb_out->transfer_buffer_length = urb_size;
 	urb_out->context = line6pcm;