sky2: leave PCI config space writeable

Since power management is done by PCI subsystem as well as driver,
don't toggle the bit that disables PCI register writes.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>