hwmon/drivers/core: Simplify complex dependency

As the thermal framework does not longer compile as a module, we can
simplify this condition below:

 if IS_REACHABLE(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF) && \
       (!defined(CONFIG_THERMAL_HWMON) || \
        !(defined(MODULE) && IS_MODULE(CONFIG_THERMAL)))

 if IS_REACHABLE(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF) && \
       (!defined(CONFIG_THERMAL_HWMON) || \
        !(defined(MODULE) && 0))

=> (whatever && 0) = 0

 if IS_REACHABLE(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF) && \
       (!defined(CONFIG_THERMAL_HWMON) || !(0))

 if IS_REACHABLE(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF) && \
       (!defined(CONFIG_THERMAL_HWMON) || 1)

=> (whatever || 1) = 1

 if IS_REACHABLE(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF) && \
       (1)

=> (whatever && 1) = whatever

 if IS_REACHABLE(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF)

CONFIG_THERMAL can not be a module anymore, then:

 if defined(CONFIG_THERMAL) && defined(CONFIG_THERMAL_OF)

And CONFIG_THERMAL_OF already depends on CONFIG_THERMAL, so:

 if defined(CONFIG_THERMAL_OF)

Thus,

 ifdef CONFIG_THERMAL_OF

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>