fixed small bug with AUDIO_ENABLED (#339)

quantum/quantum.c

@@ -435,28 +435,29 @@ void matrix_scan_quantum() {
 
   matrix_scan_kb();
 }
-
-bool is_music_on(void) {
+#ifdef AUDIO_ENABLE
+  bool is_music_on(void) {
       return (music_activated != 0);
-}
+  }
 
-void music_toggle(void) {
+  void music_toggle(void) {
       if (!music_activated) {
           music_on();
       } else {
           music_off();
       }
-}
+  }
 
-void music_on(void) {
+  void music_on(void) {
       music_activated = 1;
       music_on_user();
-}
+  }
 
-void music_off(void) {
+  void music_off(void) {
       music_activated = 0;
       stop_all_notes();
-}
+  }
 
+#endif
 __attribute__ ((weak))
 void music_on_user() {}