icside: DMA support fix

Fix problem introduced by commit 5e37bdc0 ("ide: add struct
ide_dma_ops (take 3)"): d.dma_ops shouldn't be cleared if
we are going to use DMA.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>