Staging: comedi: usbduxfast: fix checkpatch issues plus some style cleanups etc.

This patch is a major code rewrite to make checkpatch.pl happy and also
other minor things are fixed.
Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
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>