latency_analysis: Fix task name
Created by: Leo-Yan
Trace::getTaskByPid() returns task name with 'str' type, if use join() to apply for the string, it inserts comma between every chars and the task name is not readable.
So fix this by directly using name string from Trace::getTaskByPid().
Signed-off-by: Leo Yan leo.yan@linaro.org