Since tracing_on indicates only "1" (default) or "0", ftrace2bconf.sh
only need to check the value is "0".

Link: https://lkml.kernel.org/r/163077087144.222577.6888011847727968737.stgit@devnote2

Fixes: 55ed4560 ("tools/bootconfig: Add tracing_on support to helper scripts")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>