USB: rework C++-style comments

This patch (as911) replaces some C++-style commented-out debugging
lines in driver.c with a new "verbose debugging" macro.  It makes the
code look cleaner, and it's easier to turn the debugging on or off.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>