thermal: exynos: fix trips limit checking in get_th_reg()

of_thermal_get_ntrips() may return value bigger than supported
by a given SoC (i.e. on Exynos5422/5800) so fix the code to not
iterate the loop for i values >= data->ntrip.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>