iio: dac: mcp4725: Fix i2c_master_send() return value handling

The i2c_master_send() returns number of sent bytes on success,
or negative on error. The suspend/resume callbacks expect zero
on success and non-zero on error. Adapt the return value of the
i2c_master_send() to the expectation of the suspend and resume
callbacks, including proper validation of the return value.

Fixes: cf35ad61 ("iio: add mcp4725 I2C DAC driver")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230511004330.206942-1-marex@denx.de
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/mcp4725.c

@@ -47,12 +47,18 @@ static int mcp4725_suspend(struct device *dev)
 	struct mcp4725_data *data = iio_priv(i2c_get_clientdata(
 		to_i2c_client(dev)));
 	u8 outbuf[2];
+	int ret;
 
 	outbuf[0] = (data->powerdown_mode + 1) << 4;
 	outbuf[1] = 0;
 	data->powerdown = true;
 
-	return i2c_master_send(data->client, outbuf, 2);
+	ret = i2c_master_send(data->client, outbuf, 2);
+	if (ret < 0)
+		return ret;
+	else if (ret != 2)
+		return -EIO;
+	return 0;
 }
 
 static int mcp4725_resume(struct device *dev)
@@ -60,13 +66,19 @@ static int mcp4725_resume(struct device *dev)
 	struct mcp4725_data *data = iio_priv(i2c_get_clientdata(
 		to_i2c_client(dev)));
 	u8 outbuf[2];
+	int ret;
 
 	/* restore previous DAC value */
 	outbuf[0] = (data->dac_value >> 8) & 0xf;
 	outbuf[1] = data->dac_value & 0xff;
 	data->powerdown = false;
 
-	return i2c_master_send(data->client, outbuf, 2);
+	ret = i2c_master_send(data->client, outbuf, 2);
+	if (ret < 0)
+		return ret;
+	else if (ret != 2)
+		return -EIO;
+	return 0;
 }
 static DEFINE_SIMPLE_DEV_PM_OPS(mcp4725_pm_ops, mcp4725_suspend,
 				mcp4725_resume);