sky2: remove unneede workaround

This workaround is not needed. It was inherited from sk98lin driver but only
applies to an early development version of the chip that is not supported
by sky2.  The workaround required an unnecessary pci read which hurts performance

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>