Rename DownloadController's newInstance() to getInstance()

Also, make both the instance getters synchronized.

src/org/lineageos/updater/DownloadController.java

@@ -51,11 +51,11 @@ public class DownloadController implements DownloadControllerInt {
 
     private final File mDownloadRoot;
 
-    public static DownloadController getInstance() {
+    public static synchronized DownloadController getInstance() {
         return sDownloadController;
     }
 
-    public static synchronized DownloadController newInstance(Context context) {
+    public static synchronized DownloadController getInstance(Context context) {
         if (sDownloadController == null) {
             sDownloadController = new DownloadController(context);
         }

src/org/lineageos/updater/DownloadService.java

@@ -52,7 +52,7 @@ public class DownloadService extends Service {
     public void onCreate() {
         super.onCreate();
 
-        mDownloadController = DownloadController.newInstance(this);
+        mDownloadController = DownloadController.getInstance(this);
 
         mNotificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
         mNotificationBuilder = new NotificationCompat.Builder(this);