ide/isa: Replace unchecked qdev_init() by qdev_init_nofail()

isa_ide_init()'s callers don't check for failure.  isa_ide_init()
looks like it could fail, but since isa_ide_realizefn() can't fail, it
actually can't.  Replace its qdev_init() by qdev_init_nofail() to make
it obvious.

Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
