baseaudiosink: Newly added sinks don't get notified about the bin's latency

Submitted by Håvard Graff (hgr)

Link to original bug (#630441)

Description

Created attachment 170939
patch

1. make sure we have us_latency.
2. remember to subtract render_delay, as this is added on to the latency

Patch 170939, "patch":
0024-baseaudiosink-fixes-to-sync_latency.patch