Staging: comedi: usbdux: remove checkpatch.pl warnings

Fix up and remove almost all of the remaining checkpatch.pl errors
and warnings in the usbdux driver.

Cc: Bernd Porr <BerndPorr@f2s.com>
Cc: David Schleef <ds@schleef.org>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>