staging: iio: cdc: ad7746: Factor out ad7746_read_channel()

Reduce deep indenting and simplify the locking cleanup that follows.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220626122938.582107-7-jic23@kernel.org

drivers/staging/iio/cdc/ad7746.c

@@ -512,40 +512,31 @@ static int ad7746_write_raw(struct iio_dev *indio_dev,
 	return ret;
 }
 
-static int ad7746_read_raw(struct iio_dev *indio_dev,
+static int ad7746_read_channel(struct iio_dev *indio_dev,
 			       struct iio_chan_spec const *chan,
-			   int *val, int *val2,
-			   long mask)
+			       int *val)
 {
 	struct ad7746_chip_info *chip = iio_priv(indio_dev);
-	int ret, delay, idx;
-	u8 regval, reg;
+	int ret, delay;
 	u8 data[3];
+	u8 regval;
 
-	mutex_lock(&chip->lock);
-
-	switch (mask) {
-	case IIO_CHAN_INFO_RAW:
-	case IIO_CHAN_INFO_PROCESSED:
 	ret = ad7746_select_channel(indio_dev, chan);
 	if (ret < 0)
-			goto out;
+		return ret;
 	delay = ret;
 
 	regval = chip->config | AD7746_CONF_MODE_SINGLE_CONV;
-		ret = i2c_smbus_write_byte_data(chip->client, AD7746_REG_CFG,
-						regval);
+	ret = i2c_smbus_write_byte_data(chip->client, AD7746_REG_CFG, regval);
 	if (ret < 0)
-			goto out;
+		return ret;
 
 	msleep(delay);
 	/* Now read the actual register */
-
-		ret = i2c_smbus_read_i2c_block_data(chip->client,
-						    chan->address >> 8,
+	ret = i2c_smbus_read_i2c_block_data(chip->client,  chan->address >> 8,
 					    sizeof(data), data);
 	if (ret < 0)
-			goto out;
+		return ret;
 
 	*val = get_unaligned_be24(data) - 0x800000;
 
@@ -561,6 +552,27 @@ static int ad7746_read_raw(struct iio_dev *indio_dev,
 		break;
 	}
 
+	return 0;
+}
+
+static int ad7746_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2,
+			   long mask)
+{
+	struct ad7746_chip_info *chip = iio_priv(indio_dev);
+	int ret, idx;
+	u8 reg;
+
+	mutex_lock(&chip->lock);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+	case IIO_CHAN_INFO_PROCESSED:
+		ret = ad7746_read_channel(indio_dev, chan, val);
+		if (ret < 0)
+			goto out;
+
 		ret = IIO_VAL_INT;
 		break;
 	case IIO_CHAN_INFO_CALIBSCALE: