thermal: exynos: always check for critical trip points existence

* Check for critical trip point existence in exynos_tmu_initialize()
  so it is checked on all SoCs (except Exynos5433 for now).

* Use dev_err() instead of pr_err().

* Fix dev_err() to reference "device tree" not "of-thermal.c".

* Remove no longer needed check from exynos4412_tmu_initialize().

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>