net: agere: use true,false for bool variable

Fix the following coccicheck warning:

drivers/net/ethernet/agere/et131x.c:717:3-22: WARNING: Assignment of
0/1 to bool variable
drivers/net/ethernet/agere/et131x.c:721:1-20: WARNING: Assignment of
0/1 to bool variable

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Acked-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>