tracing: instance_rmdir() leaks ftrace_event_file->filter

tracing: instance_rmdir() leaks ftrace_event_file->filter

instance_rmdir() path destroys the event files but forgets to free
file->filter. Change remove_event_file_dir() to free_event_filter().

Link: http://lkml.kernel.org/p/[email protected]
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
Cc: Tom Zanussi <[email protected]>
Cc: "zhangwei(Jovi)" <[email protected]>
Cc: [email protected] # 3.11+
Fixes: f6a84bdc75b5 "tracing: Introduce remove_event_file_dir()"
Signed-off-by: Oleg Nesterov <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>