staging: comedi: adl_pci9111: sample types are unsigned

Sample values in comedi are generally represented as unsigned values.
Change the element type of the `ai_bounce_buffer[]` member of `struct
pci9111_private_data` from `short` to `unsigned short` for consistency.
Also change the type of the `array` variable in `pci9111_ai_munge()`
from `short *` to `unsigned short *`.

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