staging: line6: eliminate useless index_out variable

Playback urbs use the index_out counter to decide which part of the
playback buffer to use.  Since the urb already has a unique index in
range [0, LINE6_ISO_BUFFERS) there is no need to keep a separate
counter.

Use the urb index instead.  This also eliminates the possibility of two
urbs using the same playback buffer space if they ever complete
out-of-order for some reason.
Signed-off-by: NStefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: NMarkus Grabner <grabner@icg.tugraz.at>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/line6/pcm.h

@@ -145,11 +145,6 @@ struct snd_line6_pcm {
 	*/
 	unsigned char *buffer_in;
 
-	/**
-		 Temporary buffer index for playback.
-	*/
-	int index_out;
-
 	/**
 		 Previously captured frame (for software monitoring).
 	*/

drivers/staging/line6/playback.c

@@ -192,13 +192,10 @@ 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 +
-	    LINE6_ISO_PACKETS * line6pcm->max_packet_size * line6pcm->index_out;
+	    index * LINE6_ISO_PACKETS * line6pcm->max_packet_size;
 	urb_out->transfer_buffer_length = urb_size;
 	urb_out->context = line6pcm;
 
-	if (++line6pcm->index_out == LINE6_ISO_BUFFERS)
-		line6pcm->index_out = 0;
-
 	if (test_bit(BIT_PCM_ALSA_PLAYBACK, &line6pcm->flags) &&
 	    !test_bit(BIT_PAUSE_PLAYBACK, &line6pcm->flags)) {
 		struct snd_pcm_runtime *runtime =