udev: Add UNI-T UT-D04 multimeter cable entry.
Remove non-error hw_info_get() messages.

Currently hw_info_get() can receive requests for entries (info_id) that
the specific driver doesn't support. That is (right now) a valid
use-case and not an error (might change later, though).

Thus, for now, don't output messages for such requests at all (certainly
not as sr_err() where they show up in e.g. sigrok-cli output per default).
alsa: Check sdi and sdi->priv before derefencing them

This commit fixes bug #28