ide-disk: fix taskfile registers loading order in __ide_do_rw_disk()

Load IDE_SECTOR_REG after IDE_FEATURE_REG and IDE_NSECTOR_REG when using CHS.

This patch is basically a preparation for the next one which converts
__ide_do_rw_disk() to use struct ide_taskfile.

It shouldn't affect anything (just a usual paranoia to separate changes
which change the way in which hardware is accessed from code cleanups).

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