audio: Fix state machine initial and final state symbols

In UML, the initial state is a solid circle, the final
state is a double circle. In the Core HAL diagrams it
was the opposite.

Test: dot -Tpng stream-{in|out}-[async-]sm.gv -o ...
Change-Id: Id69f17d0a47227e744eb6dadcb5fee08c07bb0bd