Fix b/265617603: The 'breakdown by systems' list will change to 'breakdown by apps' after the user scrolls up and down.

The root cause is that the spinner was initialized many times for every
onBindViewHolder(). When the spinner is scrolled out of the screen and
scrolled back, onBindViewHolder() is triggered. The spinner selection
position was set to the mSavedSpinnerPosition. This is unexpected. Only
the first initialization should set the saved position. This fix changes
the spinner initialization to be only once.

Bug: 265617603
Fix: 265617603
Test: manual
Change-Id: I7ebd2b074cf6f560919ceec338eb8fcfaadf4d3a

src/com/android/settings/fuelgauge/batteryusage/SpinnerPreference.java

@@ -56,6 +56,10 @@ public class SpinnerPreference extends Preference {
 
     @Override
     public void onBindViewHolder(PreferenceViewHolder view) {
+        if (mSpinner != null) {
+            return;
+        }
+
         mSpinner = (Spinner) view.findViewById(R.id.spinner);
         mSpinner.setAdapter(new SpinnerAdapter(getContext(), mItems));
         mSpinner.setSelection(mSavedSpinnerPosition);