Since commit 3d439b1a ("thermal/core: Alloc-copy-free the thermal zone
parameters structure"), thermal_zone_device_register() allocates a copy
of the tzp argument and callers need not explicitly manage its lifetime.

This means the function no longer cares about the parameter being
mutable, so constify it.

No functional change.
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>