Bluetooth: Attempt to clear HCI_LE_ADV on adv set terminated error event

We should clear the flag if the adv instance removed due to receiving
this error status is the last one we have.

Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>