Correctly select peak refresh rate.

Currently we will get an arbitrary value that is greater than the
default depending on the order returned by the Display.

Bug: 180723012
Test: make RunSettingsRoboTests
      ROBOTEST_FILTER="com.android.settings.display.PeakRefreshRatePreferenceControllerTest"
Change-Id: Id2c99f2bea9c6b2814d82a9db3a417e4a93ee06d

src/com/android/settings/development/ForcePeakRefreshRatePreferenceController.java

@@ -122,7 +122,7 @@ public class ForcePeakRefreshRatePreferenceController extends DeveloperOptionsPr
     private float findPeakRefreshRate(Display.Mode[] modes) {
         float peakRefreshRate = DEFAULT_REFRESH_RATE;
         for (Display.Mode mode : modes) {
-            if (Math.round(mode.getRefreshRate()) > DEFAULT_REFRESH_RATE) {
+            if (Math.round(mode.getRefreshRate()) > peakRefreshRate) {
                 peakRefreshRate = mode.getRefreshRate();
             }
         }