iio: imu: adis16480: make sure provided frequency is positive

It could happen that either `val` or `val2` [provided from userspace] is
negative. In that case the computed frequency could get a weird value.

Fix this by checking that neither of the 2 variables is negative, and check
that the computed result is not-zero.

Fixes: e4f95939 ("iio: imu: adis16480 switch sampling frequency attr to core support")
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/adis16480.c

@@ -317,8 +317,11 @@ static int adis16480_set_freq(struct iio_dev *indio_dev, int val, int val2)
 	struct adis16480 *st = iio_priv(indio_dev);
 	unsigned int t, reg;
 
+	if (val < 0 || val2 < 0)
+		return -EINVAL;
+
 	t =  val * 1000 + val2 / 1000;
-	if (t <= 0)
+	if (t == 0)
 		return -EINVAL;
 
 	/*