gianfar: don't pass NULL dev ptr to DMA ops

Change all dma op invocations in gianfar.c to actually pass in the
device pointer.  Currently, the value is ignored, but it will be
used going forward as we implement archdata for 32-bit powerpc.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>