staging: comedi: 8255: sample types are unsigned

Sample values in comedi are generally represented as unsigned values.
`subdev_8255_interrupt()` calls `comedi_buf_put()` with a `short` data
value merely because that's what was previously expected.  Since it now
expects an `unsigned short`, change it here for consistency.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>