8139too: use true,false for bool variables

This addresses the following coccinelle warning:

drivers/net/ethernet/realtek/8139too.c:981:2-8: WARNING: Assignment of
0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>