iio: fix some warning messages

WARN_ON() only takes a condition argument.  I have changed these to
WARN() instead.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -302,7 +302,7 @@ static int iio_scan_mask_set(struct iio_dev *indio_dev,
 	if (trialmask == NULL)
 		return -ENOMEM;
 	if (!indio_dev->masklength) {
-		WARN_ON("Trying to set scanmask prior to registering buffer\n");
+		WARN(1, "Trying to set scanmask prior to registering buffer\n");
 		goto err_invalid_mask;
 	}
 	bitmap_copy(trialmask, buffer->scan_mask, indio_dev->masklength);

drivers/iio/industrialio-core.c

@@ -655,7 +655,7 @@ int __iio_device_attr_init(struct device_attribute *dev_attr,
 			break;
 		case IIO_SEPARATE:
 			if (!chan->indexed) {
-				WARN_ON("Differential channels must be indexed\n");
+				WARN(1, "Differential channels must be indexed\n");
 				ret = -EINVAL;
 				goto error_free_full_postfix;
 			}