r8169: correct phy parameters for the 8110SC

The phys of the 8110SC (RTL_GIGA_MAC_VER_{05/06}) act abnormally in
gigabit mode if they are applied the parameters in rtl8169_hw_phy_config
which actually aim the 8110S/SB.

It is ok to return early from rtl8169_hw_phy_config as it does not
apply to the 8101 and 8168 families.

Signed-off-by: Edward Hsu <edward_hsu@realtek.com.tw>
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>