Wait for devices to finish initializing when inserted, before using them. Fixes hotplug issue with XBox 360 game controller.

src/core/linux/SDL_udev.c

@@ -469,6 +469,9 @@ SDL_UDEV_Poll(void)
         action = _this->udev_device_get_action(dev);
 
         if (SDL_strcmp(action, "add") == 0) {
+            /* Wait for the device to finish initialization */
+            SDL_Delay(100);
+
             device_event(SDL_UDEV_DEVICEADDED, dev);
         } else if (SDL_strcmp(action, "remove") == 0) {
             device_event(SDL_UDEV_DEVICEREMOVED, dev);