xen/pt: Fix incomplete conversion to realize()

The conversion of "xen-pci-passthrough" to realize() (commit
5a11d0f, 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: 5a11d0f
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20181017082702.5581-17-armbru@redhat.com>

hw/xen/xen_pt.c

@@ -830,7 +830,7 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
     xen_pt_config_init(s, &err);
     if (err) {
         error_append_hint(&err, "PCI Config space initialisation failed");
-        error_report_err(err);
+        error_propagate(errp, err);
         rc = -1;
         goto err_out;
     }