isrcsubmit-cdrdao: DEFAULT_DEVICE -> get_default_device()

[JonnyJD]

There is no DEFAULT_DEVICE in python-discid anymore. This is now get_default_device(). See JonnyJD/python-discid#30.
So this script needs an update.

Although python-discid was in beta with that API (now it is stable) I am thinking about releasing 1.0.1 with DEFAULT_DEVICE as deprecated (in addition to the official get_default_device().

My isrcsubmit also uses DEFAULT_DEVICE, but only in a beta release, so this isn't a big deal there, I'd say.
I just remembered now that there was also another script using python-discid beta.