iio: frequency: ad9523: unlock on error in ad9523_reg_access()

There was a return path which got missed accidentally.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NMichael Hennerich <michael.hennerich@analog.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/frequency/ad9523.c

@@ -731,10 +731,12 @@ static int ad9523_reg_access(struct iio_dev *indio_dev,
 	} else {
 		ret = ad9523_read(indio_dev, reg | AD9523_R1B);
 		if (ret < 0)
-			return ret;
+			goto out_unlock;
 		*readval = ret;
 		ret = 0;
 	}
+
+out_unlock:
 	mutex_unlock(&indio_dev->mlock);
 
 	return ret;