r8169: simplify ocp functions

rtl8168_oob_notify is used in rtl8168dp_driver_start and
rtl8168dp_driver_stop only, so we can rename it to r8168dp_oob_notify.
The same applies to condition rtl_ocp_read_cond which can be renamed
to rtl_dp_ocp_read_cond. This allows to simplify the code.

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