r8169: fix OCP access on RTL8117

According to r8168 vendor driver DASHv3 chips like RTL8168fp/RTL8117
need a special addressing for OCP access.
Fix is compile-tested only due to missing test hardware.

Fixes: 1287723a ("r8169: add support for RTL8117")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>