net: macb: fix build break with !CONFIG_OF

This fixes the build of the macb driver that was broken by the DT changes:

drivers/net/ethernet/cadence/macb.c:1503: error: implicit declaration of function 'of_match_ptr'
drivers/net/ethernet/cadence/macb.c:1503: error: 'macb_dt_ids' undeclared here (not in a function)
drivers/net/ethernet/cadence/macb.c:1503: error: initializer element is not constant
drivers/net/ethernet/cadence/macb.c:1503: error: (near initialization for 'macb_driver.driver.of_match_table')

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>