mfd: max77686: Return correct error when pdata isn't found

When platform data is not found an -EIO (I/O error) code is returned.
This doesn't seem to be the correct error so better return -EINVAL
(Invalid argument) which is what most drivers do in this case.
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/max77686.c

@@ -129,7 +129,7 @@ static int max77686_i2c_probe(struct i2c_client *i2c,
 
 	if (!pdata) {
 		dev_err(&i2c->dev, "No platform data found.\n");
-		return -EIO;
+		return -EINVAL;
 	}
 
 	max77686 = devm_kzalloc(&i2c->dev,