tetris.kp: Modify define of global value

tetris.kp was no longer working from below.

  add argument type validate for kp_str_fmt
  commit d5d79ccb1fcd8de646bb942ecba0db84114783cb

This patch was modified by defining before the reference
to the global variable.

Signed-off-by: Tadaki SAKAI <stadaki.dev@gmail.com>