tg3: Fix 57765 B0 data corruption

The PCIe max FTS limit is too aggressive on these chips.  This patch
loosens the limit a little to eliminate data corruption issues.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>