carma-fpga: pass correct flags to ->device_prep_dma_memcpy()

DMA unmapping is handled by a driver so tell fsldma.c driver
(which is the DMA engine driver used by carma-fpga) to skip
unmapping destination and source buffers.

Cc: Ira W. Snyder <iws@ovro.caltech.edu>
Cc: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dan Williams <djbw@fb.com>