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.
This patch is to directly use name string from Trace::getTaskByPid(); and rename variable 'task_names' to 'task_name'.
Signed-off-by: Leo Yan leo.yan@linaro.org