thermal/drivers/devfreq_cooling: Fix wrong return on error path

The following error is reported by kbuild:

smatch warnings:
drivers/thermal/devfreq_cooling.c:433 of_devfreq_cooling_register_power() warn: passing zero to 'ERR_PTR'

Fix the error code by the setting the 'err' variable instead of 'cdev'.

Fixes: f8d354e821b2 ("thermal/drivers/devfreq_cooling: Use device name instead of auto-numbering")
Reported-by: kernel test robot <[e-mail]>
Reported-by: Dan Carpenter <[e-mail]>
Signed-off-by: Daniel Lezcano <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/thermal/devfreq_cooling.c

···
 	if (err < 0)
 		goto free_table;
 
-	cdev = ERR_PTR(-ENOMEM);
+	err = -ENOMEM;
 	name = kasprintf(GFP_KERNEL, "devfreq-%s", dev_name(dev));
 	if (!name)
 		goto remove_qos_req;