BACKPORT: thermal/drivers/hisi: Remove pointless lock

The threaded interrupt inspect the sensors structure to look in the temp
threshold field, but this field is read-only in all the code, except in the
probe function before the threaded interrupt is set. In other words there
is not race window in the threaded interrupt when reading the field value.

Change-Id: I457c3b546a43bcf72a3f3d8b5cb1a27172f6a834
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
(cherry picked from commit 2d4fa7b4c6f8080ced2e8237c9f46fb1fc110d64)
Signed-off-by: Kevin Wangtao <kevin.wangtao@hisilicon.com>