gpio: constify the data parameter to gpiochip_find()

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index d773540..e633a2a 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1152,8 +1152,9 @@
  * non-zero, this function will return to the caller and not iterate over any
  * more gpio_chips.
  */
-struct gpio_chip *gpiochip_find(void *data,
-				int (*match)(struct gpio_chip *chip, void *data))
+struct gpio_chip *gpiochip_find(const void *data,
+				int (*match)(struct gpio_chip *chip,
+					     const void *data))
 {
 	struct gpio_chip *chip = NULL;
 	unsigned long flags;