Use context instead of activity

Bug: 25606212
Change-Id: I5d7eca547562ab968c5f7a4b91119ee7b1c3bce5
diff --git a/src/com/android/settings/DataUsageSummary.java b/src/com/android/settings/DataUsageSummary.java
index ddf04c9..7c6f502 100644
--- a/src/com/android/settings/DataUsageSummary.java
+++ b/src/com/android/settings/DataUsageSummary.java
@@ -551,7 +551,7 @@
 
     @Override
     public void onPrepareOptionsMenu(Menu menu) {
-        final Context context = getActivity();
+        final Context context = getContext();
         final boolean appDetailMode = isAppDetailMode();
         final boolean isAdmin = mUserManager.isAdminUser();