AudioFlinger: Fix clang-tidy warning

performance-unnecessary-value-param

Test: ALLOW_LOCAL_TIDY_TRUE=1 mm -j .
Change-Id: I30481b22f5825df0ce54157b6444268c992723ef
diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index d055dd2..cc5c1e7 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -3923,7 +3923,7 @@
 sp<audioflinger::SyncEvent> AudioFlinger::createSyncEvent(AudioSystem::sync_event_t type,
                                     audio_session_t triggerSession,
                                     audio_session_t listenerSession,
-                                    audioflinger::SyncEventCallback callBack,
+                                    const audioflinger::SyncEventCallback& callBack,
                                     const wp<RefBase>& cookie)
 {
     Mutex::Autolock _l(mLock);