Staging: iio: adc: max1363_ring.c: fix up sparse warnings

Cc: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/adc/max1363_ring.c

@@ -142,7 +142,7 @@ static int max1363_ring_predisable(struct iio_dev *indio_dev)
  * then.  Some triggers will generate their own time stamp.  Currently
  * there is no way of notifying them when no one cares.
  **/
-void max1363_poll_func_th(struct iio_dev *indio_dev)
+static void max1363_poll_func_th(struct iio_dev *indio_dev)
 {
 	struct max1363_state *st = indio_dev->dev_data;