Bluetooth: MGMT: Fix holding hci_conn reference while command is queued

This removes the use of hci_conn_hold from Get Conn Info and Get Clock
Info since the callback can just do a lookup by address using the cmd
data and only then set cmd->user_data to pass to the complete callback.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>