hpt366: kill set_dma_mode() method wrapper

There's no reason to keep the set_dma_mode() method wrapper for two different
chip families, so get rid of it...

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