aaudio: fix race when disconnecting

When disconnecting more than one stream,
and the apps reopen the streams,
there was a race condition that resulted
in the first app getting a Legacy stream instead of an
MMAP stream. That is because it was disconnected before the
other streams had stopped.

Now we run the stop loop before the disconnect loop
to prevent the race.

Bug: 158316262
Test: test_steal_exclusive -r0 -d0 -s
Change-Id: Ib8efde9c2f94f6ab1ba3475d88b45d373cc8d3bb