staging: iio: ad5933: switch buffer mode to software

Since commit 152a6a884ae1 ("staging:iio:accel:sca3000 move
to hybrid hard / soft buffer design.")
the buffer mechanism has changed and the
INDIO_BUFFER_HARDWARE flag has been unused.

Since commit 2d6ca60f3284 ("iio: Add a DMAengine framework
based buffer")
the INDIO_BUFFER_HARDWARE flag has been re-purposed for
DMA buffers.

This driver has lagged behind these changes, and
in order for buffers to work, the INDIO_BUFFER_SOFTWARE
needs to be used.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Fixes: 2d6ca60f3284 ("iio: Add a DMAengine framework based buffer")
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/impedance-analyzer/ad5933.c

@@ -648,8 +648,6 @@ static int ad5933_register_ring_funcs_and_init(struct iio_dev *indio_dev)
 	/* Ring buffer functions - here trigger setup related */
 	indio_dev->setup_ops = &ad5933_ring_setup_ops;
 
-	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
-
 	return 0;
 }
 
@@ -762,7 +760,7 @@ static int ad5933_probe(struct i2c_client *client,
 	indio_dev->dev.parent = &client->dev;
 	indio_dev->info = &ad5933_info;
 	indio_dev->name = id->name;
-	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->modes = (INDIO_BUFFER_SOFTWARE | INDIO_DIRECT_MODE);
 	indio_dev->channels = ad5933_channels;
 	indio_dev->num_channels = ARRAY_SIZE(ad5933_channels);