SurfaceFlinger: use isDisplayConfigAllowed in dumpVSync()

Simplify the logic to dump the allowed display configs.

Test: adb shell dumpsys SurfaceFlinger
Change-Id: Id0c5f86779fc434f316c9da63e0118e2fc7de458
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index f7b7410..fa801af 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -813,7 +813,7 @@
     // the desired refresh rate.
     void setRefreshRateTo(RefreshRateType, Scheduler::ConfigEvent event) REQUIRES(mStateLock);
 
-    bool isDisplayConfigAllowed(int32_t configId) REQUIRES(mStateLock);
+    bool isDisplayConfigAllowed(int32_t configId) const REQUIRES(mStateLock);
 
     /*
      * Display identification