iio: convert to common i2c_check_functionality() return value

Previously most drivers that used a i2c_check_functionality() check
condition required various error codes on failure. This patchset
converts to a standard of -EOPNOTSUPP

Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/adc/mcp3422.c b/drivers/iio/adc/mcp3422.c
index ebad83e..d7b36ef 100644
--- a/drivers/iio/adc/mcp3422.c
+++ b/drivers/iio/adc/mcp3422.c
@@ -339,7 +339,7 @@
 	u8 config;
 
 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
-		return -ENODEV;
+		return -EOPNOTSUPP;
 
 	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*adc));
 	if (!indio_dev)