net: bcmgenet: modify Tx ring int_enable and int_disable vectors

Remove unnecessary function parameter priv. Use ring->priv instead.

Signed-off-by: Petri Gynther <pgynther@google.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>