pinctrl/nomadik: !CONFIG_OF build error

a60b57ed "drivers/gpio: gpio-nomadik: Add support for irqdomains" broke
building with CONFIG_OF_GPIO disabled.

Without this patch, building nhk8815_defconfig results in:

/home/arnd/linux-arm/drivers/gpio/gpio-nomadik.c: In function 'nmk_gpio_probe':
/home/arnd/linux-arm/drivers/gpio/gpio-nomadik.c:1238:6: error: 'struct gpio_chip' has no member named 'of_node'
make[3]: *** [drivers/gpio/gpio-nomadik.o] Error 1
make[2]: *** [drivers/gpio] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [drivers] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [sub-make] Error 2

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>