hw/core/machine: fix fdt memory leak

The MachineState fdt field is allocated by various machine types via
create_device_tree(), load_device_tree(), or similar, but was never
freed in machine_finalize(). Add the missing g_free() call.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20260709111249.1107640-1-marcandre.lureau@redhat.com>