net: bcmgenet: Drop useless OF code

There is nothing which needs a set of OF headers, followed by redundant
OF node ID check. Drop them for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>