PCH_GbE : Fixed the issue of checksum judgment

The checksum judgment was mistaken.
  Judgment result
     0:Correct 1:Wrong

This patch fixes the issue.

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