PowerCap: Fix an error code in powercap_register_zone()

In the current code we accidentally return the successful result from
idr_alloc() instead of a negative error pointer.  The caller is looking
for an error pointer and so it treats the returned value as a valid
pointer.

This one might be a bit serious because if it lets people get around the
kernel's protection for remapping NULL.  I'm not sure.

Fixes: 75d2364ea0ca (PowerCap: Add class driver)
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/powercap/powercap_sys.c

@@ -538,6 +538,7 @@ struct powercap_zone *powercap_register_zone(
 
 	power_zone->id = result;
 	idr_init(&power_zone->idr);
+	result = -ENOMEM;
 	power_zone->name = kstrdup(name, GFP_KERNEL);
 	if (!power_zone->name)
 		goto err_name_alloc;