staging: comedi: comedi_fops: don't export comedi_get_device_file_info()

This function is now only used in comedi_fops.c and does not need
to be exported.

Make it static and move it to avoid forward declarations.

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>