ao/audiounit: include AVAudioSession buffer in latency calc

Signed-off-by: Aman Gupta <aman@tmm1.net>

audio/out/ao_audiounit.m

@@ -155,7 +155,7 @@ static void start(struct ao *ao)
     struct priv *p = ao->priv;
     AVAudioSession *instance = AVAudioSession.sharedInstance;
 
-    p->device_latency = [instance outputLatency];
+    p->device_latency = [instance outputLatency] + [instance IOBufferDuration];
 
     OSStatus err = AudioOutputUnitStart(p->audio_unit);
     CHECK_CA_WARN("can't start audio unit");