net/macb: force endian_swp_pkt_en to off

The core has a bit for swapping packet data endianism.
Reset default from Cadence is off. Xilinx however, who uses this core on the
Zynq SoCs, opted for on.
Force it to off. This shouldn't change the behaviour for current users of the
macb, but enables usage on Zynq devices.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>