pch_gbe: Fix the issue that the receiving data is not normal.

This PCH_GBE driver had an issue that the receiving data is not normal.
This driver had not removed correctly the padding data
which the DMA include in receiving data.

This patch fixed this issue.

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