A recent dtbs_check error fix in mt6359.dtsi file changed a node name
(from "mt6359codec" to "audio-codec") without modifying the mt6539
codec code that uses it.
It leads to a probe failure after devicetree parsing returns in error:
```
[    1.354025] mt6359-sound mt6359-sound: mt6359_platform_driver_probe() failed to parse dts
[    1.355066] mt6359-sound mt6359-sound: probe with driver mt6359-sound failed with error -22
```

So, add the child node retrieval with the new name and if not found,
try with the older one for backward compatibility.

Fixes: 76b35f59 ("arm64: dts: mediatek: mt6359: fix dtbs_check error for audio-codec")
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>