staging: comedi: comedi_fops: coding style fixes

- Fixed coding style in comedi_fops.c Symbolic to octal permission.

Signed-off-by: Matias Mucciolo <mmucciolo@suteba.org.ar>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>