spapr_drc.c: do not error_report() when drc->dev->id == NULL

spapr_drc.c: do not error_report() when drc->dev->id == NULL

The error_report() call in drc_unisolate_logical() is not considering
that drc->dev->id can be NULL, and the underlying functions error_report()
calls to do its job (vprintf(), g_strdup_printf() ...) has undefined
behavior when trying to handle "%s" with NULL arguments.

Besides, there is no utility into reporting that an unknown device was
rejected by the guest.

Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20210907004755.424931-4-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>