ide: fix enabling DMA on it821x in "smart" mode

ide_tune_dma() should return '1' if IDE_HFLAG_NO_SET_MODE host flag is set.

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