thermal: samsung: Remove Exynos5440 clock handling left-overs

Commit 8014220d ("thermal: samsung: Remove support for Exynos5440")
removed the Exynos5440 specific part of code for accessing TMU interrupt
registers but the surrounding clock handling was left.

Clean it up.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>