le_audio: Correct streaming request notification for sink monitoring

This updates handling streaming request notification for sink monitoring
when there was previousely send some notification (previous status was
not empty).

Tag: #Bug
Bug: 305943737
Bug: 308171251
Test: atest bluetooth_le_audio_client_test
Change-Id: Ib7eb7bf1e27c88c6c23323fdc6a222d06438a20c