[media] export em28xx_release_resources() symbol

As reported by the kbuild test robot:

All error/warnings:

>> ERROR: "em28xx_release_resources" [drivers/media/usb/em28xx/em28xx-v4l.ko] undefined!
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx-cards.c

@@ -2839,6 +2839,7 @@ void em28xx_release_resources(struct em28xx *dev)
 	/* Mark device as unused */
 	clear_bit(dev->devno, &em28xx_devused);
 };
+EXPORT_SYMBOL_GPL(em28xx_release_resources);
 
 /*
  * em28xx_init_dev()