staging: rtl8723au: Make direct calls to GetHalDefVar8192CUsb()

Remove another round of HAL wrapping, and remove unused
SetHalDefVar8192CUsb().

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>