Staging: comedi: fix checkpatch.pl issues in comedi_test.c

This fixes almost all checkpatch.pl issues with the comedi_test.c
file.

Hint, volatile doesn't do what you think it does, it has been removed
from the structure...

Cc: Joachim Wuttke <Joachim.Wuttke@icn.siemens.de>
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>