bebob: change processing to load firmware

Previous it returns error in device probing on purpose. But this is not good
because bus reset is generated when finishing loading then device removing is
generated.

With this commit, probing is success for firmware loader but sound card
incarnation is not created.
bebob: add hardware metering to MAudio devices

All models of MAudio BeBoB devices has hardware metering and this commit
enable to get it. Currently proc interface dump it.