iio: adc: meson-saradc: unlock on error in meson_sar_adc_lock()

The meson_sar_adc_lock() function is not supposed to hold the
"indio_dev->mlock" on the error path.

Fixes: 3adbf34 ("iio: adc: add a driver for the SAR ADC found in Amlogic Meson SoCs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/meson_saradc.c

@@ -462,8 +462,10 @@ static int meson_sar_adc_lock(struct iio_dev *indio_dev)
 			regmap_read(priv->regmap, MESON_SAR_ADC_DELAY, &val);
 		} while (val & MESON_SAR_ADC_DELAY_BL30_BUSY && timeout--);
 
-		if (timeout < 0)
+		if (timeout < 0) {
+			mutex_unlock(&indio_dev->mlock);
 			return -ETIMEDOUT;
+		}
 	}
 
 	return 0;