net/fec_mpc52xx: fix BUG on missing dma_ops

The driver triggers a BUG_ON() when allocating DMA buffers because the
arch/powerpc dma_ops aren't in the net_device's struct device.  This
patch fixes the problem by using the parent of_device which does have
the correct dma_ops set.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Reviewed-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>