Bluetooth: Refactor hci_cs_le_create_conn

This patch does some code refactoring in hci_cs_le_create_conn
function. The hci_conn object is only needed in case of failure,
therefore hdev locking and hci_conn lookup were moved to
if-statement scope.

Also, the conn->state check was removed since we should always
close the connection if it fails.

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