thermal: imx: Use driver's local data to decide whether to run a measurement

Use driver's local data to evaluate the need to run or not to run a
measurement.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200703104354.19657-3-andrzej.p@collabora.com