thermal/core: Remove pointless thermal_zone_device_reset() function

The function thermal_zone_device_reset() is called in the
thermal_zone_device_register() which allocates and initialize the
structure. The passive field is already zero-ed by the allocation, the
function is useless.

Call directly thermal_zone_device_init() instead and
thermal_zone_device_reset().

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201222181110.1231977-1-daniel.lezcano@linaro.org