LeAudio: Minor variable rename

These values are defined by the BT Assigned Numbers as LE Audio specific,
but not as LC3 only types. We should name them properly to avoid any
confusion once we start adding support for other codecs.

Bug: 295972694
Test: atest --host bluetooth_le_audio_test bluetooth_le_audio_client_test bluetooth_test_broadcaster bluetooth_test_broadcaster_state_machine bluetooth_le_audio_codec_manager_test
Change-Id: I2535900425644c331e185ef29ae641a3a421c9eb