ftrace: Constify ftrace_text_reserved

Link: http://lkml.kernel.org/r/1357772960-4436-5-git-send-email-sasha.levin@oracle.com



Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>