net: atheros: remove conversion to bool in atl1c_start_mac()

No need to convert '==' expression to bool. This fixes the following
coccicheck warning:

drivers/net/ethernet/atheros/atl1c/atl1c_main.c:1189:63-68: WARNING:
conversion to bool not needed here

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