ide: don't BUG() on unsupported transfer modes

Fix ide-cris, cs5530, sc1200 and sis5513 host drivers to just return instead
of OOPS-ing for unsupported modes in ->set_dma_mode methods.

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