pinctrl: check ops->pin_config_set in pinconf_set_config()

pinconf_set_config() is called by pinctrl_gpio_set_config().
If a GPIO driver is backed by a pinctrl driver and it does not
support .pin_config_set() hook, it causes NULL pointer dereference.

Fixes: 15381bc7 ("pinctrl: Allow configuration of pins from gpiolib based drivers")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinconf.c

@@ -205,7 +205,7 @@ int pinconf_set_config(struct pinctrl_dev *pctldev, unsigned pin,
 	const struct pinconf_ops *ops;
 
 	ops = pctldev->desc->confops;
-	if (!ops)
+	if (!ops || !ops->pin_config_set)
 		return -ENOTSUPP;
 
 	return ops->pin_config_set(pctldev, pin, configs, nconfigs);