bitbake/lib/bb/data_smart.py: Double OVERRIDE expansion fix

bitbake/lib/bb/data_smart.py: Double OVERRIDE expansion fix

    INITSCRIPT_PARAMS_${PN}_slugos. We will expandKeys
    and end up with INITSCRIPT_PARAMS_busybox_slugos
    then (we have slugos in OVERRIDES) and we get
    INITSCRIPT_PARAMS_busybox. Now adding busybox to OVERRIDES
    and nothing changed. The reason is simple. The update_data
    code is using __getitem__ and __setitem__ to access
    the data object. This method does not pay the cookie
    monster. This is why we don't know that for the OVERRIDE
    busybox INITSCRIPT_PARAMS is available. We now pay the
    cookie monster and it looks better