thermal/drivers/mtk_thermal: Remove redundant initializations of several variables

Several variables are being initialized with values that is never
read and being updated later with a new value. The initializations
are redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210422120412.246291-1-colin.king@canonical.com