[TG3]: Clear GPIO mask before storing.

The GPIO settings may change during reset and so the stored values in
tp->grc_local_ctrl should be cleared first.

Signed-off-by: Gary Zambrano <zambrano@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>