tracing: Change apply_subsystem_event_filter() paths to check file->system == dir

tracing: Change apply_subsystem_event_filter() paths to check file->system == dir

filter_free_subsystem_preds(), filter_free_subsystem_filters() and
replace_system_preds() can simply check file->system->subsystem and
avoid strcmp(call->class->system).

Better yet, we can pass "struct ftrace_subsystem_dir *dir" instead of
event_subsystem and just check file->system == dir.

Thanks to Namhyung Kim who pointed out that replace_system_preds() can
be changed too.

Link: http://lkml.kernel.org/p/[email protected]
Signed-off-by: Oleg Nesterov <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>