BACKPORT: thermal/drivers/hisi: Remove mutex_lock in the code

The mutex is used to protect against writes in the configuration register.

That happens at probe time, with no possible race yet.

Then when the module is unloaded and at suspend/resume.

When the module is unloaded, it is an userspace operation, thus via a process.
Suspending the system goes through the freezer to suspend all the tasks
synchronously before continuing. So it is not possible to hit the suspend ops
in this driver while we are unloading it.

The resume is the same situation than the probe.

In other words, even if there are several places where we write the
configuration register, there is no situation where we can write it at the same
time, so far as I can judge

Change-Id: Ie71c809f485240dbf463b142fe0f3ab1d2fae2ae
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
(cherry picked from commit cc1ab38d2b2ad3290426c2234cf83e7a323554c7)
Signed-off-by: Kevin Wangtao <kevin.wangtao@hisilicon.com>