libata: add missing call to ->cable_detect() in new EH path

->cable_detect() used to be called on by the old ata_bus_probe() path.
Add invocation to ata_eh_revalidate_and_attach() right after IDENTIFYs
are done.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>