gpio: fix "gpio-line-names" property retrieval

Following commit 9427ecbed4 ("gpio: Rework of_gpiochip_set_names()
to use device property accessors"), "gpio-line-names" DT property is
not retrieved anymore when chip->parent is not set by the driver.
This is due to OF based property reads having been replaced by device
based property reads.

This patch fixes that by making use of
fwnode_property_read_string_array() instead of
device_property_read_string_array() and handing over either
of_fwnode_handle(chip->of_node) or dev_fwnode(chip->parent)
to that function.

Fixes: 9427ecbed4 ("gpio: Rework of_gpiochip_set_names() to use device property accessors")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-of.c

@@ -493,7 +493,8 @@ int of_gpiochip_add(struct gpio_chip *chip)
 
 	/* If the chip defines names itself, these take precedence */
 	if (!chip->names)
-		devprop_gpiochip_set_names(chip);
+		devprop_gpiochip_set_names(chip,
+					   of_fwnode_handle(chip->of_node));
 
 	of_node_get(chip->of_node);