Bluetooth: Remove unnecessary hcon->smp_conn variable

Bluetooth: Remove unnecessary hcon->smp_conn variable

The smp_conn member of struct hci_conn was simply a pointer to the
l2cap_conn object. Since we already have hcon->l2cap_data that points to
the same thing there's no need to have this second variable. This patch
removes it and changes the single place that was using it to use
hcon->l2cap_data instead.

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