r8169: fix firmware not resetting tp->ocp_base

Typically the firmware takes care that tp->ocp_base is reset to its
default value. That's not the case (at least) for RTL8117.
As a result subsequent PHY access reads/writes the wrong page and
the link is broken. Fix this be resetting tp->ocp_base explicitly.

Fixes: 229c1e0d ("r8169: load firmware for RTL8168fp/RTL8117")
Reported-by: Aaron Ma <mapengyu@gmail.com>
Tested-by: Aaron Ma <mapengyu@gmail.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>