libata: schedule probing after SError access failure during autopsy

If SError isn't accessible, EH can't tell whether hotplug has happened
or not.  Report SError read failure with AC_ERR_OTHER and schedule
probing with hardreset.  This will be mainly useful for PMPs.

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