vfio: Avoid error_propagate() after migrate_add_blocker()

vfio: Avoid error_propagate() after migrate_add_blocker()

When migrate_add_blocker(blocker, &err) is followed by
error_propagate(errp, err), we can often just as well do
migrate_add_blocker(..., errp).  This is the case in
vfio_migration_probe().

Prior art: commit 386f6c07d2 "error: Avoid error_propagate() after
migrate_add_blocker()".

Cc: Kirti Wankhede <kwankhede@nvidia.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210720125408.387910-8-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed by: Kirti Wankhede <kwankhede@nvidia.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>