tracing: Rename struct ftrace_subsystem_dir to trace_subsystem_dir

The name "ftrace" really refers to the function hook infrastructure. It
is not about the trace_events. The structure ftrace_subsystem_dir holds
the information about trace event subsystems. It should not be named
ftrace, rename it to trace_subsystem_dir.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 1561779..d4ad58e 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -313,7 +313,7 @@
 }
 
 struct trace_array;
-struct ftrace_subsystem_dir;
+struct trace_subsystem_dir;
 
 enum {
 	FTRACE_EVENT_FL_ENABLED_BIT,
@@ -355,7 +355,7 @@
 	struct event_filter		*filter;
 	struct dentry			*dir;
 	struct trace_array		*tr;
-	struct ftrace_subsystem_dir	*system;
+	struct trace_subsystem_dir	*system;
 	struct list_head		triggers;
 
 	/*