HID: wacom: wacom_setup_numbered_buttons is local to wacom_wac

wacom_setup_numbered_buttons() is not used outside of wacom_wac.c,
make it static.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.c

@@ -2711,7 +2711,7 @@ int wacom_setup_touch_input_capabilities(struct input_dev *input_dev,
 	return 0;
 }
 
-void wacom_setup_numbered_buttons(struct input_dev *input_dev,
+static void wacom_setup_numbered_buttons(struct input_dev *input_dev,
 				int button_count)
 {
 	int i;