LeAudio: Minor structure usage cleanup

Instead of duplicating one structure internals into the other, lets
use the enclosing type directly. That reduces fragmentation and
simplifies copying/assignments.

Bug: 388733112
Test: atest --host bluetooth-test-audio-hal-le-audio-software bluetooth-test-audio-hal-aidl-leaudio-utils bluetooth_le_audio_test bluetooth_le_audio_client_test  bluetooth_test_broadcaster bluetooth_test_broadcaster_state_machine bluetooth_le_audio_codec_manager_test net_test_btif net_test_btif_hh net_test_btif_stack
Flag: EXEMPT; mechanical refactor - no logical change
Change-Id: I3ba5d4ea0ad811a53906184105e8f7fb47fffe76