bebob: fix mappling for MIDI conformant data in stream channels

This is for devices which has usual firmware and some MIDI ports.

This is an output from M-Audio Ozonic.
$ ./firewire-request /dev/fw1 fcp 01ff02c000000000ff03ffff
0cff02c0 00000000ff 03 03 02 0101 0302 02 0201 0402 02 0501 0502

This output means that two MIDI ports use the same channels in stream.
But previous parser return ENOSYS for this device.