sky2: phy power down needs PCI config write enabled

In order to change PCI registers (via the iomap'd window),
it needs to be enabled; this wasn't being done in sky2_phy_power
the function that turns on/off power to the PHY.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>