Fix playback start with sync_ptr mode

Fix by Istvan Varadi <ivaradi@gmail.com>

- start the playback with snd_pcm_hw_start failed with -EPIPE, because
 some pointers were not updated. I attached a patch for alsa-lib 1.0.8,
 in which sync_ptr is called before SNDRV_PCM_IOCTL_START. It seems to
 solve the problem, though I don't know alsa-lib enough to be sure that
 this is the right solution...

src/pcm/pcm_hw.c

@@ -543,6 +543,7 @@ static int snd_pcm_hw_start(snd_pcm_t *pcm)
 	assert(pcm->stream != SND_PCM_STREAM_PLAYBACK ||
 	       snd_pcm_mmap_playback_hw_avail(pcm) > 0);
 #endif
+	sync_ptr(hw, 0);
 	if (ioctl(hw->fd, SNDRV_PCM_IOCTL_START) < 0) {
 		err = -errno;
 		SYSMSG("SNDRV_PCM_IOCTL_START failed");