Staging: comedi: Fixed coding style issues.

comedi_fops.c : A forward decleration was declared as extern although it
                is a function private to this file. Changed the
                decleration to static.

Signed-off-by: Mark Pearson <markpearson_de@yahoo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>