bebob: Simplify the way to generate address for Music Subunit

BeBoB driver doesn't use commands for the other types of subunit.
firewire-lib/bebob: make it error to receive zero length of AV/C response
firewire-lib/bebob/oxfw: Improve codes of commands for easily reading
bebob: Improve codes for discover

Correct some miunderstanding about BridgeCo specification.
bebob: Improve codes to discover M-Audio special firmware

It can be shortened with loop and table.
fireworks: fix line over 80 characters

According to checkpatch.pl
bebob: Improve comments and codes

Minor updates.