thermal: exynos: remove redundant pdata checks from exynos_tmu_control()

pdata->reference_voltage and pdata->gain are always defined
to non-zero values so remove the redundant checks from
exynos_tmu_control().

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