rsi: fix a typo "throld" -> "threshold"

There is a typo in debug message. Fix it.
s/throld/threshold

Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1585837078-6149-1-git-send-email-hqjagain@gmail.com