trm290: use custom ->dma_{start,end} to handle trm290_prepare_drive()

Use custom ->dma_{start,end} methods to handle trm290_prepare_drive()
there instead of in ->dma_setup method.

There should be no functional changes caused by this patch
(DMA support is disabled currently in trm290.c).

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>