Just in case somebody else is struggling to get this working, the easiest way is to create a /etc/modprobe.d/btusb.conf with the following:
install btusb modprobe ath3k; /bin/echo "13d3 3304" >> /sys/bus/drivers/ath3k/new_id; modprobe --ignore-install btusb
This will load the ath3k module before btusb is loaded and tell the module to search also for devices with the id "13d3 3304".
