r8169: remove rtl_wol_pll_power_down

rtl_wol_pll_power_down() is used in only one place and removing it
makes the code simpler and better readable.

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