ide: cleanup generic_ide_ioctl()

* Fix intendation for the main 'switch ()'.

* 'switch ()' -> 'if ()' for HDIO_DRIVE_TASKFILE case.

* Move HDIO_SET_NICE case under HDIO_GET_NICE one.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>