Bluetooth: Fix Get Conn Info to use cmd_complete callback

This patch fixes the Get Connection Information mgmt command to take
advantage of the new cmd_complete callback. This allows for great
simplifications in the logic for constructing the cmd_complete event.

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