iio: fix some warning messages

WARN_ON() only takes a condition argument.  I have changed these to
WARN() instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index d7e908a..0f6f63b 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -302,7 +302,7 @@
 	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);