There is an extra log "error_setg" in qdev_add_device(). When
hot-plug a device, if the corresponding bus doesn't exist, it
will trigger an asseration "assert(*errp == NULL)".
Fixes: 515a7970490 (log: Add some logs on VM runtime path)
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
