PM: sleep: wakeup: Skip wakeup_source_sysfs_remove() if device is not there

Skip wakeup_source_sysfs_remove() to fix a NULL pinter dereference via
ws->dev, if the wakeup source is unregistered before registering the
wakeup class from device_add().

Fixes: 2ca3d1ecb8 ("PM / wakeup: Register wakeup class kobj after device is added")
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
[ rjw: Subject & changelog, white space ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/wakeup.c

@@ -244,7 +244,9 @@ void wakeup_source_unregister(struct wakeup_source *ws)
 {
 	if (ws) {
 		wakeup_source_remove(ws);
-		wakeup_source_sysfs_remove(ws);
+		if (ws->dev)
+			wakeup_source_sysfs_remove(ws);
+
 		wakeup_source_destroy(ws);
 	}
 }