IIO: ADC: fix return value check in stm32_dfsdm_adc_probe()

In case of error, the function devm_iio_device_alloc() returns NULL
pointer not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.

Fixes: e2e6771 ("IIO: ADC: add STM32 DFSDM sigma delta ADC support")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/iio/adc/stm32-dfsdm-adc.c

@@ -1100,9 +1100,9 @@ static int stm32_dfsdm_adc_probe(struct platform_device *pdev)
 	dev_data = (const struct stm32_dfsdm_dev_data *)of_id->data;
 
 	iio = devm_iio_device_alloc(dev, sizeof(*adc));
-	if (IS_ERR(iio)) {
+	if (!iio) {
 		dev_err(dev, "%s: Failed to allocate IIO\n", __func__);
-		return PTR_ERR(iio);
+		return -ENOMEM;
 	}
 
 	adc = iio_priv(iio);