A bug was found in the new DMA engine for the 57766.  This patch
disables it, which causes the device to fallback to the old DMA engine.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Reviewed-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>