FIX: mhiramat said "put echo 0 > tracing on _before_ reading out trace"

However, only these two lines is seen in the trace.
Too fewer than expected.

 4)   0.033 us    |      thin_put();
 4)   0.022 us    |      thin_put();

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>