pinctrl: stmfx: Fix compile issue when CONFIG_OF_GPIO is not defined
When CONFIG_GPIO_OF is not defined, struct gpio_chip 'of_node' member does
not exist:
drivers/pinctrl/pinctrl-stmfx.c: In function 'stmfx_pinctrl_probe':
drivers/pinctrl/pinctrl-stmfx.c:652:17: error: 'struct gpio_chip' has no member named 'of_node'
pctl->gpio_chip.of_node = np;