hwmon: (core) Avoid cyclic dependency between hwmon and thermal_sys

If both hwmon and thermal_sys are built as modules, and
CONFIG_THERMAL_HWMON is enabled, the following cyclic module dependency
is reported.

depmod: ERROR: Found 2 modules in dependency cycles!
depmod: ERROR: Cycle detected: hwmon -> thermal_sys -> hwmon

Fixes: e4bce763adb2 ("hwmon: (core) New hwmon registration API")
Reported-by: Vignesh R <vigneshr@ti.com>
Cc: Keerthy J <j-keerthy@ti.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>