gpio: nomadik: Add missing IS_ERR() check

The function gpio_device_get_desc() can return an error pointer and is
not checked for one. Add check for error pointer.

Fixes: ddeb66d2cb10f ("gpio: nomadik: don't print out global GPIO numbers in debugfs callbacks")
Cc: [e-mail]
Signed-off-by: Ethan Tidmore <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-nomadik.c

···
 #ifdef CONFIG_PINCTRL_NOMADIK
 	if (mode == NMK_GPIO_ALT_C && pctldev) {
 		desc = gpio_device_get_desc(chip->gpiodev, offset);
+		if (IS_ERR(desc))
+			return;
+
 		mode = nmk_prcm_gpiocr_get_mode(pctldev, desc_to_gpio(desc));
 	}
 #endif