Bluetooth: SMP: Fix variable dereferenced before check 'conn'

This fixes kbuild findings:

smatch warnings:
net/bluetooth/smp.c:1633 smp_user_confirm_reply() warn: variable
dereferenced before check 'conn' (see line 1631)
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/smp.c

@@ -1628,11 +1628,11 @@ int smp_user_confirm_reply(struct hci_conn *hcon, u16 mgmt_op, __le32 passkey)
 	u32 value;
 	int err;
 
-	bt_dev_dbg(conn->hcon->hdev, "");
-
 	if (!conn)
 		return -ENOTCONN;
 
+	bt_dev_dbg(conn->hcon->hdev, "");
+
 	chan = conn->smp;
 	if (!chan)
 		return -ENOTCONN;