gpiolib: make gpiochip_get_desc() public

It makes sense for a GPIO driver to want to get its own descriptor
without requesting it. After all, the driver knows that it'll still be
valid. Let's move this helper to linux/gpio/driver.h.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -757,6 +757,8 @@ struct gpio_desc *gpiochip_request_own_desc(struct gpio_chip *gc,
 					    enum gpiod_flags dflags);
 void gpiochip_free_own_desc(struct gpio_desc *desc);
 
+struct gpio_desc *gpiochip_get_desc(struct gpio_chip *gc, unsigned int hwnum);
+
 #ifdef CONFIG_GPIOLIB
 
 /* lock/unlock as IRQ */