staging: comedi: comedi_compat32.h: checkpatch.pl --strict cleanup

Fix the checkpatch.pl --strict issues:

CHECK: extern prototypes should be avoided in .h files

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>