gpio: Fix range check in of_gpio_simple_xlate()

of_gpio_simple_xlate() has an off-by-one bug where it checks to see if
args[0] is > ngpio instead of >=.  args[0] must always be less than
ngpio because it is a zero-based enumeration.
Signed-off-by: Roland Stigge <stigge@antcom.de>
[grant.likely: beef up commit text]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/of/gpio.c

@@ -140,7 +140,7 @@ int of_gpio_simple_xlate(struct gpio_chip *gc,
 	if (WARN_ON(gpiospec->args_count < gc->of_gpio_n_cells))
 		return -EINVAL;
 
-	if (gpiospec->args[0] > gc->ngpio)
+	if (gpiospec->args[0] >= gc->ngpio)
 		return -EINVAL;
 
 	if (flags)