iio: iio: Fix iio_channel_read return if channel havn't info

When xilinx-xadc is used with hwmon driver to read voltage, offset used
for temperature is always applied whatever the channel.

iio_channel_read must return an error to avoid offset for channel
without IIO_CHAN_INFO_OFFSET property.
Signed-off-by: Fabien Proriol <fabien.proriol@jdsu.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/inkern.c

@@ -426,6 +426,9 @@ static int iio_channel_read(struct iio_channel *chan, int *val, int *val2,
 	if (val2 == NULL)
 		val2 = &unused;
 
+	if(!iio_channel_has_info(chan->channel, info))
+		return -EINVAL;
+
 	if (chan->indio_dev->info->read_raw_multi) {
 		ret = chan->indio_dev->info->read_raw_multi(chan->indio_dev,
 					chan->channel, INDIO_MAX_RAW_ELEMENTS,