hmp-cmd: fix a missing_break warning

hmp-cmd: fix a missing_break warning

This fix coverity issues 94417686:
    1260        break;
    CID 94417686: (MISSING_BREAK)
    1261. unterminated_case: The case for value "MIGRATION_PARAMETER_THROTTLE_TRIGGER_THRESHOLD" is not terminated by a 'break' statement.
    1261    case MIGRATION_PARAMETER_THROTTLE_TRIGGER_THRESHOLD:
    1262        p->has_throttle_trigger_threshold = true;
    1263        visit_type_int(v, param, &p->throttle_trigger_threshold, &err);
    1264    case MIGRATION_PARAMETER_CPU_THROTTLE_INITIAL:

Fixes: dc14a470763c96fd9d360e1028ce38e8c3613a77
Fixes: Coverity (CID 1421950)
Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
Message-Id: <20200318071620.59748-1-pannengyuan@huawei.com>
Reviewed-by: Keqian Zhu <zhukeqian1@huawei.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>