tracing: Mark tracing_dentry_percpu() static

Nothing outside of kernel/trace/trace.c references tracing_dentry_percpu().

Link: http://lkml.kernel.org/r/1353302917-13995-7-git-send-email-josh@joshtriplett.org



Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>