Bluetooth: Lookup hci_conn in hci_le_conn_complete_evt

This patch does a trivial code refactoring in hci_conn lookup in
hci_le_conn_complete_evt. It performs the hci_conn lookup at the
begining of the function since it is used by both flows (error
and success).

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>