gpio: change gpiochip_request_own_desc() prototype

The current prototype of gpiochip_request_own_desc() requires to obtain
a pointer to a descriptor. This is in contradiction to all other GPIO
request schemes, and imposes an extra step of obtaining a descriptor to
drivers. Most drivers actually cannot even perform that step since the
function that does it (gpichip_get_desc()) is gpiolib-private.

Change gpiochip_request_own_desc() to return a descriptor from a
(chip, hwnum) tuple and update users of this function (currently
gpiolib-acpi only).

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index e78a237..a2de58ff 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -166,7 +166,8 @@
 
 #endif /* CONFIG_GPIO_IRQCHIP */
 
-int gpiochip_request_own_desc(struct gpio_desc *desc, const char *label);
+struct gpio_desc *gpiochip_request_own_desc(struct gpio_chip *chip, u16 hwnum,
+					    const char *label);
 void gpiochip_free_own_desc(struct gpio_desc *desc);
 
 #else /* CONFIG_GPIOLIB */