os: decrease Audio::PERIOD to lower latency

To archive lower latency the length of a period was reduced from
2048 (~46ms) to 512 (~11.6ms) samples.

It should be noted that this change probably breaks audio in Qemu on
most systems.

Issue #1644.

repos/os/include/audio_out_session/audio_out_session.h

@@ -50,7 +50,7 @@ namespace Audio_out {
 
 	enum {
 		QUEUE_SIZE  = 16,            /* buffer queue size */
-		PERIOD      = 2048,          /* samples per period */
+		PERIOD      = 512,           /* samples per period (~11.6ms) */
 		SAMPLE_RATE = 44100,
 		SAMPLE_SIZE = sizeof(float),
 	};