Thermal device attributes may still be opened after unregistering
the thermal zone and deleting the thermal device.

Currently there is no protection against accessing thermal device
operations after unregistering a thermal zone. To enable adding
such protection, protect the device delete operation with the
thermal zone device mutex. This requires splitting the call to
device_unregister() into its components, device_del() and put_device().
Only the first call can be executed under mutex protection, since
put_device() may result in releasing the thermal zone device memory.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>