gpio: delete unneeded test before of_node_put

Of_node_put supports NULL as its argument, so the initial test is not
necessary.

Suggested by Uwe Kleine-König.

The semantic patch that fixes this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression e;
@@

-if (e)
   of_node_put(e);
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-of.c

@@ -307,7 +307,5 @@ void of_gpiochip_add(struct gpio_chip *chip)
 void of_gpiochip_remove(struct gpio_chip *chip)
 {
 	gpiochip_remove_pin_ranges(chip);
-
-	if (chip->of_node)
 	of_node_put(chip->of_node);
 }