OmniControl: workaround for style background staying

no idea what caused this
starts to happen after QPR3 merge
set explicit background for grid fragment
TODO: check in future if still needed but no harm to keep it

Change-Id: I3532505ada0a32f515d3b15f37e72c4393b36bd4
diff --git a/app/src/main/res/layout/grid_fragment.xml b/app/src/main/res/layout/grid_fragment.xml
index 67ade28..b381af9 100644
--- a/app/src/main/res/layout/grid_fragment.xml
+++ b/app/src/main/res/layout/grid_fragment.xml
@@ -5,4 +5,5 @@
     android:layout_height="match_parent"
     android:gravity="center"
     android:numColumns="@integer/grid_view_columns"
+    android:background="?android:attr/colorBackground"
     android:stretchMode="columnWidth"/>