ide: convert "empty" REQ_TYPE_ATA_CMD requests to use REQ_TYPE_ATA_TASKFILE

Based on the previous work by Tejun Heo.

There should be no functionality changes caused by this patch.

Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>