iio:imu:adis16400 remove an unneeded check

We know "ret" is zero here so there is no need to check.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/imu/adis16400_core.c

@@ -281,7 +281,7 @@ static ssize_t adis16400_write_frequency(struct device *dev,
 	st->variant->set_freq(st, val);
 	mutex_unlock(&indio_dev->mlock);
 
-	return ret ? ret : len;
+	return len;
 }
 
 /* Power down the device */