iio: querying buffer scan_mask should return 0/1

Ensure that querying the IIO buffer scan_mask returns a value of
0 or 1. Currently querying the scan mask has the value returned
by test_bit(), which returns either true or false. For some
architectures test_bit() may return -1 for true, which will appear
to return an error when returning from iio_scan_mask_query().

Additionally, it's important for the sysfs interface to consistently
return the same thing when querying the scan_mask.

Signed-off-by: Alec Berg <alecaberg@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -165,7 +165,8 @@ static ssize_t iio_scan_el_show(struct device *dev,
 	int ret;
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 
-	ret = test_bit(to_iio_dev_attr(attr)->address,
+	/* Ensure ret is 0 or 1. */
+	ret = !!test_bit(to_iio_dev_attr(attr)->address,
 		       indio_dev->buffer->scan_mask);
 
 	return sprintf(buf, "%d\n", ret);
@@ -866,7 +867,8 @@ int iio_scan_mask_query(struct iio_dev *indio_dev,
 	if (!buffer->scan_mask)
 		return 0;
 
-	return test_bit(bit, buffer->scan_mask);
+	/* Ensure return value is 0 or 1. */
+	return !!test_bit(bit, buffer->scan_mask);
 };
 EXPORT_SYMBOL_GPL(iio_scan_mask_query);