thermal/drivers/exynos: Remove an unnecessary field description

It seems that the field has been removed in one of the previous commits,
but the description has been forgotten.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Mateusz Majewski <m.majewski2@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20231201095625.301884-2-m.majewski2@samsung.com