a_bus_probe()

Commit f58229f8060055b08b34008ea08f31de1e2f003c accidentally made
ata_bus_probe() not use reverse order probing.  Fix it.

There currently isn't any PATA driver which uses obsolete
ata_bus_probe() path, so this patch is mainly for correctness.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>