Take a look at this thread and follow the instructions near the end of it:
https://bbs.archlinux.org/viewtopic.php?id=271357
If that doesn't help then give the solutions in here a try:
https://askubuntu.com/questions/148481/how-do-i-prevent-immediate-wake-up-from-suspend-and-or-hibernation-from-pci-devi