Bluetooth: ISO: clear iso_data always when detaching conn from hcon

Bluetooth: ISO: clear iso_data always when detaching conn from hcon

When setting conn->hcon = NULL, also conn->hcon->iso_data = NULL is
necessary, otherwise later iso_conn_free() will UAF.

Fix clearing of iso_data in iso_sock_disconn()

Fixes KASAN: slab-use-after-free in iso_conn_hold_unless_zero on
iso_sock_release() followed by hci_abort_conn_sync().

Fixes: fbdc4bc47268 ("Bluetooth: ISO: Use defer setup to separate PA sync and BIG sync")
Signed-off-by: Pauli Virtanen <pav@iki.fi>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>