debug: use dev_WARN() rather than WARN_ON() in device_pm_add()

device_pm_add() has a WARN_ON that is showing relatively high on
kerneloops.org, but unfortunately the WARN_ON is less than useful
in that it doesn't print any information about what device is causing
the issue.

This patch fixes this by turning the WARN_ON() into the newly
introduces dev_WARN() which will print information about the
device in question.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/power/main.c

@@ -83,7 +83,7 @@ void device_pm_add(struct device *dev)
 		 * transition is in progress in order to avoid leaving them
 		 * unhandled down the road
 		 */
-		WARN_ON(true);
+		dev_WARN(dev, "Parentless device registered during a PM transaction\n");
 	}
 
 	list_add_tail(&dev->power.entry, &dpm_list);