le_audio: Change dialer sounds to SOUNDEFFECTS instead of MEDIA

MEDIA causes handover from broadcast to unicast which is not expected
in dialer usage. There is no reason to use MEDIA for such sounds.

Bug: 377856052
Test: atest bluetooth_le_audio_client_test --host
Flag: EXEMPT; simple fix
Change-Id: Ie5ab5834dfd5e44fcb3f38fc7bbd14e6f50d56a1