staging:iio:ad7192: Mark channels as unsigned

The values reported by the AD7793 are unsigned.
	In uniploar mode:
			0x000000 is zeroscale
			0xffffff is fullscale
	In bipolar mode:
			0x000000 is negative fullscale
			0x800000 is zeroscale
			0xffffff is positive fullscale

In bipolar mode there is a binary offset, but the values are still unsigned.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/ad7192.c

@@ -945,7 +945,7 @@ static const struct iio_info ad7195_info = {
 	  IIO_CHAN_INFO_SCALE_SHARED_BIT,				\
 	  .address = _address,						\
 	  .scan_index = _si,						\
-	  .scan_type =  IIO_ST('s', 24, 32, 0)}
+	  .scan_type =  IIO_ST('u', 24, 32, 0)}
 
 #define AD7192_CHAN(_chan, _address, _si)				\
 	{ .type = IIO_VOLTAGE,						\
@@ -955,7 +955,7 @@ static const struct iio_info ad7195_info = {
 	  IIO_CHAN_INFO_SCALE_SHARED_BIT,				\
 	  .address = _address,						\
 	  .scan_index = _si,						\
-	  .scan_type =  IIO_ST('s', 24, 32, 0)}
+	  .scan_type =  IIO_ST('u', 24, 32, 0)}
 
 #define AD7192_CHAN_TEMP(_chan, _address, _si)				\
 	{ .type = IIO_TEMP,						\
@@ -965,7 +965,7 @@ static const struct iio_info ad7195_info = {
 	  IIO_CHAN_INFO_SCALE_SEPARATE_BIT,				\
 	  .address = _address,						\
 	  .scan_index = _si,						\
-	  .scan_type =  IIO_ST('s', 24, 32, 0)}
+	  .scan_type =  IIO_ST('u', 24, 32, 0)}
 
 static struct iio_chan_spec ad7192_channels[] = {
 	AD7192_CHAN_DIFF(1, 2, NULL, AD7192_CH_AIN1P_AIN2M, 0),