net: bcmgenet: remove netif_carrier_off from adjust_link

The bcmgenet_mii_setup() function is registered as the adjust_link
callback from the phylib for the GENET driver.

The phylib always sets the netif_carrier according to phydev->link
prior to invoking the adjust_link callback, so there is no need to
repeat that in the link down case within the network driver.

Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>