r8169: revert part of 6dccd16b

The 8169/8110SC currently announces itself as:
[...]
eth0: RTL8169sc/8110sc at 0x........, ..:..:..:..:..:.., XID 18000000 IRQ ..
                                                             ^^^^^^^^
It uses RTL_GIGA_MAC_VER_05 and this part of the changeset can cut
its performance by a factor of 2~2.5 as reported by Timo.

(the driver includes code just before the hunk to write the ChipCmd
register when mac_version == RTL_GIGA_MAC_VER_0[1-4])

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Timo Jantunen <jeti@welho.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>