net: bcmgenet: Use correct dev_id for free_irq

bcmgenet_open()'s error path call free_irq() with a dev_id argument
different from the one we used to call request_irq() with, this will
make us trip over the warning in kernel/irq/manage.c:__free_irq()

Fixes: 1c1008c7

 ("net: bcmgenet: add main driver file")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>