net: bcmgenet: add begin/complete ethtool ops

Make sure clock is enabled for ethtool ops.

Fixes: 1c1008c7 ("net: bcmgenet: add main driver file")
Signed-off-by: Edwin Chan <edwin.chan@broadcom.com>
Signed-off-by: Doug Berger <opendmb@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>