Fix "battery saver" not in the top seaching result for indexing

Bug: 204964119
Test: make SettingsRoboTests
Change-Id: Ifbbf979abe9e96e7af66ec20173e996793d2703e

src/com/android/settings/fuelgauge/BatterySaverController.java

@@ -63,7 +63,7 @@ public class BatterySaverController extends BasePreferenceController
 
     @Override
     public int getAvailabilityStatus() {
-        return AVAILABLE_UNSEARCHABLE;
+        return AVAILABLE;
     }
 
     @Override

tests/robotests/src/com/android/settings/fuelgauge/BatterySaverControllerTest.java

@@ -117,4 +117,10 @@ public class BatterySaverControllerTest {
 
         assertThat(mBatterySaverController.getSummary()).isEqualTo("Off");
     }
+
+    @Test
+    public void getAvailabilityStatus_returnAvailable() {
+        assertThat(mBatterySaverController.getAvailabilityStatus())
+                .isEqualTo(BatterySaverController.AVAILABLE);
+    }
 }