hw/cxl: Ensure there is enough data to read the input header in cmd_get_physical_port...

hw/cxl: Ensure there is enough data to read the input header in cmd_get_physical_port_state()

If len_in is smaller than the header length then the accessing the
number of ports will result in an out of bounds access.
Add a check to avoid this.

Reported-by: Esifiel <esifiel@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20241101133917.27634-11-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>