ALSA: ali5451: Fix out-of-bound position reporting

BugLink: http://bugs.launchpad.net/bugs/1634153

commit db685779 upstream.

The pointer callbacks of ali5451 driver may return the value at the
boundary occasionally, and it results in the kernel warning like
  snd_ali5451 0000:00:06.0: BUG: , pos = 16384, buffer size = 16384, period size = 1024

It seems that folding the position offset is enough for fixing the
warning and no ill-effect has been seen by that.
Reported-by: Enrico Mioso <mrkiko.rs@gmail.com>
Tested-by: Enrico Mioso <mrkiko.rs@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

sound/pci/ali5451/ali5451.c

@@ -1408,6 +1408,7 @@ snd_ali_playback_pointer(struct snd_pcm_substream *substream)
 	spin_unlock(&codec->reg_lock);
 	dev_dbg(codec->card->dev, "playback pointer returned cso=%xh.\n", cso);
 
+	cso %= runtime->buffer_size;
 	return cso;
 }
 
@@ -1428,6 +1429,7 @@ static snd_pcm_uframes_t snd_ali_pointer(struct snd_pcm_substream *substream)
 	cso = inw(ALI_REG(codec, ALI_CSO_ALPHA_FMS + 2));
 	spin_unlock(&codec->reg_lock);
 
+	cso %= runtime->buffer_size;
 	return cso;
 }