[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>