iio: adc: cc10001: Fix regulator_get_voltage() return value check

regulator_get_voltage() returns a non-negative value in case of success,
and a negative error in case of error. Let's fix this.

Fixes: 1664f6a5 ("iio: adc: Cosmic Circuits 10001 ADC driver")
Signed-off-by: Naidu Tellapati <naidu.tellapati@imgtec.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/cc10001_adc.c

@@ -230,7 +230,7 @@ static int cc10001_adc_read_raw(struct iio_dev *indio_dev,
 
 	case IIO_CHAN_INFO_SCALE:
 		ret = regulator_get_voltage(adc_dev->reg);
-		if (ret)
+		if (ret < 0)
 			return ret;
 
 		*val = ret / 1000;