stm: disable audio function in systick.

stm/systick.c

@@ -15,8 +15,8 @@ void sys_tick_init(void) {
 void SysTick_Handler(void) {
     sys_tick_counter++;
     // hack!
-    void audio_drain(void);
-    audio_drain();
+    //void audio_drain(void);
+    //audio_drain();
 }
 
 void sys_tick_delay_ms(uint32_t delay_ms) {