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 <[e-mail]>
Signed-off-by: Markus Grabner <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/line6/playback.c

···
 	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;