net: bcmgenet: Fix error handling on IRQ retrieval

This fixes the error handling for the mandatory IRQs. There is no need
for the error message anymore, this is now handled by platform_get_irq.

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