hw/pci-bridge/cxl_downstream: Fix type naming mismatch

hw/pci-bridge/cxl_downstream: Fix type naming mismatch

Fix capitalization difference between struct name and typedef.

Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Gregory Price <gregory.price@memverge.com>
Tested-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20230206172816.8201-3-Jonathan.Cameron@huawei.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>