Bluetooth: Fix crash when ioctl(HCIUARTSETPROTO) fails

If the fail happens the HCI del_timer may timeout after the the hci dev
unregister. This lead to a kernel crash.

Reported-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>