net: bcmgenet: remove bogus tx queue checks

netdev_pick_tx already takes care of making sure that a given
skb->queue_mapping value will remain within the number of advertised
hardware queue number, there is no need to re-do this again in the
driver.

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