atrace: fix Sync Manager tracing preventing enabling of kernel sync tracing

Both Sync Manager tracing and kernel sync tracing were using "sync" to
enable tracing and since Sync Manager was found first, this prevented
enabling kernel sync tracing.

To fix this, use "syncman" to enable Sync Manager tracing.

Change-Id: Id3b799e01e5041c582cd752c8c40d3e36954f821
Signed-off-by: Iliyan Malchev <malchev@google.com>