Fix jank after adding a widget for lock screen

After adding a widget, you see a black flash, but
there's also a small sliver of wallpaper left
showing. This change covers up that small bit 
of wallpaper.

Bug: 7381803
diff --git a/res/layout/keyguard_appwidget_picker_layout.xml b/res/layout/keyguard_appwidget_picker_layout.xml
index b678925..e533672 100644
--- a/res/layout/keyguard_appwidget_picker_layout.xml
+++ b/res/layout/keyguard_appwidget_picker_layout.xml
@@ -18,8 +18,8 @@
         android:id="@+id/layout_root"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
-        android:layout_marginLeft="@dimen/keyguard_appwidget_picker_margin_left"
-        android:layout_marginRight="@dimen/keyguard_appwidget_picker_margin_right"
+        android:paddingLeft="@dimen/keyguard_appwidget_picker_margin_left"
+        android:paddingRight="@dimen/keyguard_appwidget_picker_margin_right"
         android:paddingTop="2dip"
         android:paddingBottom="2dip"
         android:orientation="vertical" >