thermal: core: Fix NULL pointer dereference in zone registration error path

[ Upstream commit 04e6ccfc93c5a1aa1d75a537cf27e418895e20ea ]

If device_register() in thermal_zone_device_register_with_trips()
returns an error, the tz variable is set to NULL and subsequently
dereferenced in kfree(tz->tzp).

Commit adc8749b15 ("thermal/drivers/core: Use put_device() if
device_register() fails") added the tz = NULL assignment in question to
avoid a possible double-free after dropping the reference to the zone
device.  However, after commit 4649620d9404 ("thermal: core: Make
thermal_zone_device_unregister() return after freeing the zone"), that
assignment has become redundant, because dropping the reference to the
zone device does not cause the zone object to be freed any more.

Drop it to address the NULL pointer dereference.

Fixes: 3d439b1a2a ("thermal/core: Alloc-copy-free the thermal zone parameters structure")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/thermal/thermal_core.c

@@ -1382,7 +1382,6 @@ unregister:
 	device_del(&tz->device);
 release_device:
 	put_device(&tz->device);
-	tz = NULL;
 remove_id:
 	ida_free(&thermal_tz_ida, id);
 free_tzp: