The conversion of "xen-pci-passthrough" to realize() (commit
5a11d0f7, v2.6.0) neglected to convert the xen_pt_config_init()
error path.  If xen_pt_config_init() fails, xen_pt_realize() reports
the error, then returns success without completing its job.  I don't
know the exact impact, but it can't be good.

Belatedly convert the error path.

Fixes: 5a11d0f7
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Acked-by: NAnthony PERARD <anthony.perard@citrix.com>
Message-Id: <20181017082702.5581-17-armbru@redhat.com>