LeAudio: Minor argument passing improvement

Pass a single direction data to SetMetadataToAse() instead of the
bidirectional container, since just a single direction is needed.
Also pass by reference if possible.

Bug: 308428860
Bug: 295972694
Test: atest bluetooth_le_audio_test bluetooth_le_audio_client_test  bluetooth_test_broadcaster bluetooth_test_broadcaster_state_machine bluetooth_le_audio_codec_manager_test
Flag: EXEMPT; mechanical refactor - verified by the unit tests
Change-Id: I20d44988628882caf507e72d47fb40e65125ca92