Distinguish systrace timelines for playback and capture

Bug: 30120068
Change-Id: If416540f0785e83e7b1e8ba986ee55b5b9298a2a
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index 2547746..5609c86 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -6036,7 +6036,7 @@
 
             // sleep with mutex unlocked
             if (sleepUs > 0) {
-                ATRACE_BEGIN("sleep");
+                ATRACE_BEGIN("sleepC");
                 mWaitWorkCV.waitRelative(mLock, microseconds((nsecs_t)sleepUs));
                 ATRACE_END();
                 sleepUs = 0;