thermal: exynos: remove redundant threshold_code checks from exynos_tmu_initialize()

Remove runtime checks for negative return values of temp_to_code()
from exynos_tmu_initialize().

The current level temperature data hardcoded in pdata will never
cause a negative temp_to_code() return values and checking itself
is not proper.  The checks in question are done at runtime in
a production code for data that is hardcoded inside driver during
development time and later it doesn't change.  Such data should
be verified during development and review time (i.e. by a script
parsing relevant data from exynos_tmu_data.c, one can also argue
that verification to be done is so simple that the review by
a maintainer should be enough).

Theres 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>
Tested-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>