rspiusb driver cleanup - remove dbg macro

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Greg, 
I think my last patch was broken because I forgot to turn plain text in my mailer. 
Here is the new patch. Let me know if it is in good enough shape to make it in the tree. 
I am preparing other patches in the same driver to address some of the other TODO points. 
At some point in this work I will looking for someone with a Princeton Instrument Camera for test. 

Best regards

Jean-Pierre Sainfeld