thermal: exynos: use sanitize_temp_error() in exynos7_tmu_initialize()

Fix sanitize_temp_error() to handle Exynos7 SoCs and then use it in
exynos7_tmu_initialize().

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>