[Bluetooth] Fix unintentional fall-through in HCI line discipline

A trivial fix to (what looks like) an unintentional fall-through in the
HCI line discipline.

Signed-off-by: Ohad Ben-Cohen <ohad@bencohen.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>