Skip triggering an LSI when the AER root error status is updated if no
LSI is defined for the device. We can have a root bridge with no LSI,
MSI and MSI-X defined, for example on POWER systems.

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Message-Id: <20211116170133.724751-4-fbarrat@linux.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>