r8169: remove unneeded check in r8168_pll_power_down

RTL_GIGA_MAC_VER_23/24 are configured by rtl_hw_start_8168cp_2()
and rtl_hw_start_8168cp_3() respectively which both apply
CPCMD_QUIRK_MASK, thus clearing bit ASF.

Bit ASF isn't set at any other place in the driver, therefore this
check can be removed.

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