uboot-d1: fix build with swig 4.3.0

uboot-d1: fix build with swig 4.3.0

Swig 4.3.0 has changed SWIG_Python_AppendOutput, which now requires an
additional parameter `is_void`. SWIG_AppendOutput remains unchanged.
This was fixed upstream in u-boot/u-boot@a63456b

```
scripts/dtc/pylibfdt/libfdt_wrap.c: In function ‘_wrap_fdt_next_node’:
scripts/dtc/pylibfdt/libfdt_wrap.c:5581:17: error: too few arguments to function ‘SWIG_Python_AppendOutput’
 5581 |     resultobj = SWIG_Python_AppendOutput(resultobj, val);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~
```

This is the same fix as applied in 363e07d.

Fixes: #20619
Link: #20620
Signed-off-by: Trix Taiclet <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20620
Signed-off-by: Hauke Mehrtens <[email protected]>