SurfaceFlinger: return DisplayStatInfo from getDisplayStatInfo

Code cleanup - return the class instead of passing it as an
output parameter.

Test: SF unit tests
Change-Id: I7a995415a81f3944d93a1cb573c8e3108464bd07
diff --git a/services/surfaceflinger/Scheduler/Scheduler.h b/services/surfaceflinger/Scheduler/Scheduler.h
index c4e1edf..403d9bc 100644
--- a/services/surfaceflinger/Scheduler/Scheduler.h
+++ b/services/surfaceflinger/Scheduler/Scheduler.h
@@ -101,7 +101,7 @@
     void setDuration(ConnectionHandle, std::chrono::nanoseconds workDuration,
                      std::chrono::nanoseconds readyDuration);
 
-    void getDisplayStatInfo(DisplayStatInfo* stats, nsecs_t now);
+    DisplayStatInfo getDisplayStatInfo(nsecs_t now);
 
     // Returns injector handle if injection has toggled, or an invalid handle otherwise.
     ConnectionHandle enableVSyncInjection(bool enable);