iio: adc: twl4030: Disable the vusb3v1 rugulator in the error handling path of 'twl4030_madc_probe()'

Commit 7cc97d77ee8a has introduced a call to 'regulator_disable()' in the
.remove function.
So we should also have such a call in the .probe function in case of
error after a successful 'regulator_enable()' call.

Add a new label for that and use it.

Fixes: 7cc97d77ee8a ("iio: adc: twl4030: Fix ADC[3:6] readings")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/twl4030-madc.c

@@ -899,11 +899,13 @@ static int twl4030_madc_probe(struct platform_device *pdev)
 	ret = iio_device_register(iio_dev);
 	if (ret) {
 		dev_err(&pdev->dev, "could not register iio device\n");
-		goto err_i2c;
+		goto err_usb3v1;
 	}
 
 	return 0;
 
+err_usb3v1:
+	regulator_disable(madc->usb3v1);
 err_i2c:
 	twl4030_madc_set_current_generator(madc, 0, 0);
 err_current_generator: