hw/cxl/cxl-host: Fix segmentation fault when getting cxl-fmw property

hw/cxl/cxl-host: Fix segmentation fault when getting cxl-fmw property

QEMU crashes (Segmentation fault) when getting cxl-fmw property via
qmp:

(QEMU) qom-get path=machine property=cxl-fmw

This issue is caused by accessing wrong callback (opaque) type in
machine_get_cfmw().

cxl_machine_init() sets the callback as `CXLState *` type but
machine_get_cfmw() treats the callback as
`CXLFixedMemoryWindowOptionsList **`.

Fix this error by casting opaque to `CXLState *` type in
machine_get_cfmw().

Fixes: 03b39fcf64bc ("hw/cxl: Make the CXL fixed memory window setup a machine parameter.")
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Xingtao Yao <yaoxt.fnst@fujitsu.com>
Link: https://lore.kernel.org/r/20240704093404.1848132-1-zhao1.liu@linux.intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20240705113956.941732-2-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>