thermal: exynos: simplify temp_to_code() and code_to_temp()

* Remove dead temp check from temp_to_code() (this function users
  in exynos_tmu_initialize() always pass correct temperatures and
  exynos_tmu_set_emulation() returns early for EXYNOS4210 because
  TMU_SUPPORT_EMULATION flag is not set on this SoC).

* Move temp_code check from code_to_temp() to exynos_tmu_read()
  (code_to_temp() only user).

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Tested-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>