r8169: remove unused constant RsvdMask

Since 9d3679fe

 ("r8169: inline rtl8169_make_unusable_by_asic")
this constant isn't used any longer, so remove it.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>