parallel: parallel_hds_isa_init() shouldn't fail

It shouldn't fail, and no caller checks for failure.  Make failure
fatal.

Maintainers of affected machines cc'ed.

Cc: Anthony Liguori <aliguori@amazon.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Leon Alrae <leon.alrae@imgtec.com>
Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
