net: fec: use managed DMA API functions to allocate BD ring

So it gets freed when the device is going away.
This fixes a DMA memory leak on driver probe() fail and driver
remove().

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed