pch_gbe: Fixed the issue on which PC was frozen when link was downed.

When a link was downed during network use,
there is an issue on which PC freezes.

This patch fixed this issue.

Signed-off-by: Toshiharu Okada <toshiharu-linux@dsn.okisemi.com>
Signed-off-by: David S. Miller <davem@davemloft.net>