gpiolib: Remove 'const' from data argument of gpiochip_find()

Commit 3d0f7cf0 "gpio: Adjust of_xlate API to support multiple GPIO
chips" changed the api of gpiochip_find to drop const from the data
parameter of the match hook, but didn't also drop const from data
causing a build warning.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 1ba08f0..365ea09 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -142,7 +142,7 @@
 /* add/remove chips */
 extern int gpiochip_add(struct gpio_chip *chip);
 extern int __must_check gpiochip_remove(struct gpio_chip *chip);
-extern struct gpio_chip *gpiochip_find(const void *data,
+extern struct gpio_chip *gpiochip_find(void *data,
 					int (*match)(struct gpio_chip *chip,
 						     void *data));