HDMI: RequestActiveSource's callback updates local AS only when invalid

The local active source may have already been changed by another action before the RequestActiveSource action is complete. This extra check provides more confidence that the TV needs to broadcast <Active Source> and helps to avoid future bugs if a new way of updating the active source is added.

Bug: 315141766
Test: atest HdmiCecLocalDeviceTvTest
Change-Id: Ied4bdfa5e74239ae28c18fff8b7beee8919353a9