thermal/drivers/rcar: Replace spin_lock_irqsave by spin_lock in hard IRQ

On RT or even on mainline with 'threadirqs' on the command line all
interrupts which are not explicitly requested with IRQF_NO_THREAD
run their handlers in thread context. The same applies to soft interrupts.
That means they are subject to the normal scheduler rules and no other
code is going to acquire that lock from hard interrupt context either,
so the irqsave() here is pointless in all cases.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1603760790-37748-1-git-send-email-tiantao6@hisilicon.com