iio:ti_am335x: 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>
Cc: Zubair Lutfullah <zubair.lutfullah@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/ti_am335x_adc.c

@@ -166,7 +166,7 @@ static int tiadc_buffer_preenable(struct iio_dev *indio_dev)
 	for (i = 0; i < fifo1count; i++)
 		read = tiadc_readl(adc_dev, REG_FIFO1);
 
-	return iio_sw_buffer_preenable(indio_dev);
+	return 0;
 }
 
 static int tiadc_buffer_postenable(struct iio_dev *indio_dev)