staging:iio:ade7758: Remove redundant call to iio_sw_buffer_preenable()

The equivalent of iio_sw_buffer_preenable() is now done in the IIO buffer core,
so there is no need to do this from the driver anymore.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/meter/ade7758_ring.c

@@ -87,15 +87,10 @@ static int ade7758_ring_preenable(struct iio_dev *indio_dev)
 {
 	struct ade7758_state *st = iio_priv(indio_dev);
 	unsigned channel;
-	int ret;
 
 	if (!bitmap_empty(indio_dev->active_scan_mask, indio_dev->masklength))
 		return -EINVAL;
 
-	ret = iio_sw_buffer_preenable(indio_dev);
-	if (ret < 0)
-		return ret;
-
 	channel = find_first_bit(indio_dev->active_scan_mask,
 				 indio_dev->masklength);