hw/cxl: Use a switch to explicitly check size in caps_reg_read()

hw/cxl: Use a switch to explicitly check size in caps_reg_read()

Bring this read function inline with the others that do
check for unexpected size values.

Also reduces line lengths to sub 80 chars.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Message-Id: <20231023140210.3089-2-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>