gpio: sim: Declare gpio_sim_hog_config_item_ops static

Compiler is not happy:

  warning: symbol 'gpio_sim_hog_config_item_ops' was not declared. Should it be static?

Fixes: cb8c474e ("gpio: sim: new testing module")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

drivers/gpio/gpio-sim.c

@@ -1322,7 +1322,7 @@ static void gpio_sim_hog_config_item_release(struct config_item *item)
 	kfree(hog);
 }
 
-struct configfs_item_operations gpio_sim_hog_config_item_ops = {
+static struct configfs_item_operations gpio_sim_hog_config_item_ops = {
 	.release	= gpio_sim_hog_config_item_release,
 };