iio: at91: fix error return code in at91_adc_probe()

Fix to return -ENODEV instead of 0 if non-TSMR adc don't
support, as done elsewhere in this function.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: NJosh Wu <josh.wu@atmel.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/iio/adc/at91_adc.c

@@ -1047,6 +1047,7 @@ static int at91_adc_probe(struct platform_device *pdev)
 	} else {
 		if (!st->caps->has_tsmr) {
 			dev_err(&pdev->dev, "We don't support non-TSMR adc\n");
+			ret = -ENODEV;
 			goto error_disable_adc_clk;
 		}