gpiolib: export gpiochip_get_desc

The function was currently used internal by the gpiolib. Since commit
56cc3af4 ("pinctrl: da9062: add driver support") it is also used by
drivers so we need to export the symbol.
Signed-off-by: NMarco Felsch <m.felsch@pengutronix.de>
Link: https://lore.kernel.org/r/20200225093102.10964-1-m.felsch@pengutronix.deSigned-off-by: NLinus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -149,6 +149,7 @@ struct gpio_desc *gpiochip_get_desc(struct gpio_chip *chip,
 
 	return &gdev->descs[hwnum];
 }
+EXPORT_SYMBOL_GPL(gpiochip_get_desc);
 
 /**
  * desc_to_gpio - convert a GPIO descriptor to the integer namespace