Error -2 is ENOENT (No such file or directory). The driver queries the display
for audio-related information, while my display does not have speakers nor
headset connector.

Paul, can you confirm that you are also using a DisplayPort cable and that your
display does not have speakers?

I suspect that the "error" is pretty much expected in this case and the driver
is being too verbose about it. Either the calling code should consider -ENOENT
as a non-error, or the helper functions should simply return 0 when no
audio-related data is available from the display.