Fix background bleeding in splash scren image view

Re-add the @null background on the splash screen icon image view to
ensure we don't display the windowBackground in the image view

Test: Manually tested with faulty apps (SwiftKey, Whatsapp, Splitwise)
Bug: 195433420
Change-Id: I4e489b203ff30385112dbc4aa60c4b6aceb4d6b0