USB: a bit more coding style cleanup

I was sitting in a train threatened to be blocked by ice. I took this
as a hint to do some more boring work for the common good. Here's
a bit more for coding style.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>