Pass the destination File to the callback

The current argument is unused and it should have been removed
with commit 81229329f1
("Generate download clients using a builder class"). Instead of
removing it completely, use it to pass the File of the download.

src/org/lineageos/updater/controller/UpdaterController.java

@@ -176,7 +176,7 @@ public class UpdaterController implements UpdaterControllerInt {
             }
 
             @Override
-            public void onSuccess(String body) {
+            public void onSuccess(File destination) {
                 Log.d(TAG, "Download complete");
                 UpdateDownload update = mDownloads.get(downloadId).mUpdate;
                 update.setStatus(UpdateStatus.VERIFYING);