In case thermal_zone_xxx_register() returns an error, priv->zone
isn't NULL any more, but contains the error code.
This is passed to thermal_zone_device_unregister(), then. This checks
for priv->zone being NULL, but the error code is != NULL. So it works
with the error code as a pointer. Crashing immediately.
To fix this, reset priv->zone to NULL before entering
rcar_gen3_thermal_remove().