A small fix to be able to get rid of debug messages

[bluetech]

I personally prefer DEBUG, because I like to keep asserts on even in production. However, we don't use them here, so it hardly matters.

[dvdhrm]

Pulled. Thanks.

I don't like assert()s. kmscon should always properly cleanup the VT and assert()s don't allow proper termination. Otherwise, we have to manually reset the VT which is disturbing. Hence, I prefer decent error-handling. Therefore, I just reused NDEBUG.

Thanks David