Bluetooth: Audio: Get function for bt_audio_codec_qos_pref.

Get the preferred QoS settings via bt_bap_ep_get_info()
Therefore no need to use the internal header file to get it.

This PR fixes https://github.com/zephyrproject-rtos/zephyr/issues/72359



Signed-off-by: Ping Wang <pinw@demant.com>