Bluetooth: hci_conn: Check non NULL function before calling for HFP offload

For some controllers such as QCA2066, it does not need to send
HCI_Configure_Data_Path to configure non-HCI data transport path to support
HFP offload, their device drivers may set hdev->get_codec_config_data as
NULL, so Explicitly add this non NULL checking before calling the function.

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