bgmac: fix device initialization on Northstar SoCs (condition typo)

On Northstar (Broadcom's ARM architecture) we need to manually enable
all cores. Code for that is already in place, but the condition for it
was wrong.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>