Bluetooth: hci_conn: Fix memory leaks

When hci_cmd_sync_queue() failed in hci_le_terminate_big() or
hci_le_big_terminate(), the memory pointed by variable d is not freed,
which will cause memory leak. Add release process to error path.

Fixes: eca0ae4a ("Bluetooth: Add initial implementation of BIS connections")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>