iio: adc: ad_sigma_delta: fix buffered mode irq

Buffered mode using ad_sigma_delta is not functional as the IRQ is not
enabled in the postenable callback for devices that are not using
spi_engine (INDIO_BUFFER_HARDWARE mode).

Comparing to the 2022_R2 version, it seems that the condition should
have been negated.

Fix by checking inequality instead of equality to INDIO_BUFFER_HARDWARE.

Fixes: 27b588f ("Merge tag 'xilinx-v2023.1' of https://github.com/Xilinx/linux-xlnx.git")
Signed-off-by: Dumitru Ceclan <dumitru.ceclan@analog.com>

Author: dumitruceclan

drivers/iio/adc/ad_sigma_delta.c

@@ -450,7 +450,7 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 	 * Differs from upstream because of the spi engine support and we want to enable
 	 * the irq only after setting AD_SD_MODE_CONTINUOUS (as in the upstream lib)
 	 */
-	if (iio_device_get_current_mode(indio_dev) == INDIO_BUFFER_HARDWARE) {
+	if (iio_device_get_current_mode(indio_dev) != INDIO_BUFFER_HARDWARE) {
 		sigma_delta->irq_dis = false;
 		enable_irq(sigma_delta->irq_line);
 	}