iio: adc: checking for NULL instead of IS_ERR() in probe

mcb_request_mem() returns an ERR_PTR(), it doesn't return NULL.

Fixes: 74aeac4da66f ('iio: adc: Add MEN 16z188 ADC driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: Stable@vger.kernel.org

drivers/iio/adc/men_z188_adc.c

@@ -121,8 +121,8 @@ static int men_z188_probe(struct mcb_device *dev,
 	indio_dev->num_channels = ARRAY_SIZE(z188_adc_iio_channels);
 
 	mem = mcb_request_mem(dev, "z188-adc");
-	if (!mem)
-		return -ENOMEM;
+	if (IS_ERR(mem))
+		return PTR_ERR(mem);
 
 	adc->base = ioremap(mem->start, resource_size(mem));
 	if (adc->base == NULL)