acpi: thermal: Don't call thermal_zone_device_is_enabled()

thermal_zone_device_update() can now handle disabled thermal zones, so
the check here is not needed.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200703104354.19657-2-andrzej.p@collabora.com