staging: comedi: don't expose struct comedi_device_file_info

This structure is only used in comedi_fops.c as part of handling
the file operations and sysfs files. Remove it's defenition from
comedidev.h so it's not exposed to the comedi drivers.

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>