thermal/drivers/exynos: Use BIT wherever possible

The original driver did not use that macro and it allows us to make our
intentions slightly clearer.

Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Mateusz Majewski <m.majewski2@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20231201095625.301884-9-m.majewski2@samsung.com