Fix the issue of null previous brightness reason in the logs

Bug: 268459499
Test: Manually verified the logs are now as expected
Change-Id: I88a8be939d15d60d9e90df62909fa9b0031ca199

services/core/java/com/android/server/display/DisplayPowerController2.java

@@ -1148,6 +1148,7 @@ final class DisplayPowerController2 implements AutomaticBrightnessController.Cal
         final int previousPolicy;
         boolean mustInitialize = false;
         int brightnessAdjustmentFlags = 0;
+        mBrightnessReasonTemp.set(null);
         mTempBrightnessEvent.reset();
         SparseArray<DisplayPowerControllerInterface> displayBrightnessFollowers;
         synchronized (mLock) {

services/core/java/com/android/server/display/brightness/BrightnessEvent.java

@@ -100,7 +100,7 @@ public final class BrightnessEvent {
      * A utility to reset the BrightnessEvent to default values
      */
     public void reset() {
-        mReason.set(null);
+        mReason = new BrightnessReason();
         mTime = SystemClock.uptimeMillis();
         mPhysicalDisplayId = "";
         // Lux values