overlays: Fix background colouring for settings themed icons

 * Settings dashboard icons use primary colour as background since https://github.com/LineageOS/android_packages_apps_Settings/commit/1c376a3a10db9db94c0719263d9018c6cf8749d3


 * Google forgot to apply it in their themed icons, making them look odd

Change-Id: I45ef6b8cd7ed1a89a811fac6066df7bcdbdf56a6
Signed-off-by: Adithya R <gh0strider.2k18.reborn@gmail.com>