pinctrl: core: Add missing #ifdef CONFIG_GPIOLIB

To fix the following build warnings when CONFIG_GPIOLIB=n.

drivers/pinctrl/core.c:1607:20: warning: unused variable 'chip' [-Wunused-variable]
 1608 |  struct gpio_chip *chip;
      |                    ^~~~
drivers/pinctrl/core.c:1606:15: warning: unused variable 'gpio_num' [-Wunused-variable]
 1607 |  unsigned int gpio_num;
      |               ^~~~~~~~
drivers/pinctrl/core.c:1605:29: warning: unused variable 'range' [-Wunused-variable]
 1606 |  struct pinctrl_gpio_range *range;
      |                             ^~~~~

Fixes: f1b206cf

 ("pinctrl: core: print gpio in pins debugfs file")
Signed-off-by: He Zhe <zhe.he@windriver.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20201028103921.22486-1-zhe.he@windriver.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>