staging: comedi: comedi_test: make samples unsigned

Represent the fake samples as unsigned shorts instead of signed shorts,
as this is the usual Comedi convention.  There is no change to the
actual binary representation, although the `cfc_write_to_buffer()` call
currently expects a signed short for some bizarre reason.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/comedi_test.c

@@ -85,7 +85,8 @@ static const struct comedi_lrange waveform_ai_ranges = {
 	 }
 };
 
-static short fake_sawtooth(struct comedi_device *dev, unsigned int range_index,
+static unsigned short fake_sawtooth(struct comedi_device *dev,
+				    unsigned int range_index,
 				    unsigned long current_time)
 {
 	struct waveform_private *devpriv = dev->private;
@@ -109,7 +110,7 @@ static short fake_sawtooth(struct comedi_device *dev, unsigned int range_index,
 	return offset + value;
 }
 
-static short fake_squarewave(struct comedi_device *dev,
+static unsigned short fake_squarewave(struct comedi_device *dev,
 				      unsigned int range_index,
 				      unsigned long current_time)
 {
@@ -131,15 +132,17 @@ static short fake_squarewave(struct comedi_device *dev,
 	return offset + value;
 }
 
-static short fake_flatline(struct comedi_device *dev, unsigned int range_index,
+static unsigned short fake_flatline(struct comedi_device *dev,
+				    unsigned int range_index,
 				    unsigned long current_time)
 {
 	return dev->read_subdev->maxdata / 2;
 }
 
 /* generates a different waveform depending on what channel is read */
-static short fake_waveform(struct comedi_device *dev, unsigned int channel,
-			   unsigned int range, unsigned long current_time)
+static unsigned short fake_waveform(struct comedi_device *dev,
+				    unsigned int channel, unsigned int range,
+				    unsigned long current_time)
 {
 	enum {
 		SAWTOOTH_CHAN,