Input: gpio-keys - report error when disabling unsupported key

When trying to disable a key that is not supported by the device we should
report error, not do nothing and report success:

root@yocto:/sys/devices/soc0/gpio-keys# cat keys
114-116
root@yocto:/sys/devices/soc0/gpio-keys# echo 77 > keys
root@yocto:/sys/devices/soc0/gpio-keys#

We want 'echo 77 > keys' to report an error, but silence to give us an
illusion that all is 'ok'.
Signed-off-by: Peng Fan <van.freenix@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/keyboard/gpio_keys.c

@@ -239,6 +239,11 @@ static ssize_t gpio_keys_attr_store_helper(struct gpio_keys_drvdata *ddata,
 		}
 	}
 
+	if (i == ddata->pdata->nbuttons) {
+		error = -EINVAL;
+		goto out;
+	}
+
 	mutex_lock(&ddata->disable_lock);
 
 	for (i = 0; i < ddata->pdata->nbuttons; i++) {