staging: comedi: adv_pci1723: sample types are unsigned

Sample values in comedi are generally represented as unsigned values.
Change the element type of the `ao_data[]` member of `struct
pci1723_private` from `short` to `unsigned short` for consistency.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/adv_pci1723.c

@@ -105,7 +105,7 @@ configures all channels in the same group.
 
 struct pci1723_private {
 	unsigned char da_range[8];	/* D/A output range for each channel */
-	short ao_data[8];	/* data output buffer */
+	unsigned short ao_data[8];	/* data output buffer */
 };
 
 /*