gpiolib: change a warning to debug message when failing to get gpio

It's the drivers responsibility to react on failure to get
the gpio descriptors and not the frameworks. Since there are
some common peripherals that may or may not have certain
pins connected to gpio lines, depending on the platform,
printing the warning there may end up generating useless bug
reports.
Signed-off-by: NHeikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -2447,7 +2447,7 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
 	}
 
 	if (IS_ERR(desc)) {
-		dev_warn(dev, "lookup for GPIO %s failed\n", con_id);
+		dev_dbg(dev, "lookup for GPIO %s failed\n", con_id);
 		return desc;
 	}