Bluetooth: Fix missing rcu_read_unlock() in hci_bdaddr_is_paired()

When finding a matching LTK the rcu_read_unlock() function was failing
to release the RCU read lock. This patch adds the missing call to
rcu_reaD_unlock().

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>