ALSA: vx: Don't try to update capture stream before running

The update of stream costs significantly, and we should avoid it
unless the stream really has started.  Check pipe->running flag
instead of pipe->prepared.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/vx/vx_pcm.c

@@ -1015,7 +1015,7 @@ static void vx_pcm_capture_update(struct vx_core *chip, struct snd_pcm_substream
 	int size, space, count;
 	struct snd_pcm_runtime *runtime = subs->runtime;
 
-	if (! pipe->prepared || (chip->chip_status & VX_STAT_IS_STALE))
+	if (!pipe->running || (chip->chip_status & VX_STAT_IS_STALE))
 		return;
 
 	size = runtime->buffer_size - snd_pcm_capture_avail(runtime);