r8169: improve rtl_pcie_state_l2l3_enable

All calls to this function have the enable parameter set to false.
So we can replace the function with a disable-only version.

v2:
- fixed copy & paste error

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