orinoco: do not resgister NULL pm_notifier function

With DEBUG_NOTIFIERS it results in

[11330.890966] WARNING: at /home/bor/src/linux-git/kernel/notifier.c:88
notifier_call_chain+0x91/0xa0()
[11330.890977] Hardware name: PORTEGE 4000
[11330.890983] Invalid notifier called! ...

Without DEBUG_NOTIFIERS it most likely crashes on NULL pointer.
Signed-off-by: Andrey Borzenkov <arvidjaar@mail.ru>
Acked-by: David Kilroy <kilroyd@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/orinoco/orinoco.c

@@ -3157,8 +3157,20 @@ static int orinoco_pm_notifier(struct notifier_block *notifier,
 
 	return NOTIFY_DONE;
 }
+
+static void orinoco_register_pm_notifier(struct orinoco_private *priv)
+{
+	priv->pm_notifier.notifier_call = orinoco_pm_notifier;
+	register_pm_notifier(&priv->pm_notifier);
+}
+
+static void orinoco_unregister_pm_notifier(struct orinoco_private *priv)
+{
+	unregister_pm_notifier(&priv->pm_notifier);
+}
 #else /* !PM_SLEEP || HERMES_CACHE_FW_ON_INIT */
-#define orinoco_pm_notifier NULL
+#define orinoco_register_pm_notifier(priv) do { } while(0)
+#define orinoco_unregister_pm_notifier(priv) do { } while(0)
 #endif
 
 /********************************************************************/
@@ -3648,8 +3660,7 @@ struct net_device
 	priv->cached_fw = NULL;
 
 	/* Register PM notifiers */
-	priv->pm_notifier.notifier_call = orinoco_pm_notifier;
-	register_pm_notifier(&priv->pm_notifier);
+	orinoco_register_pm_notifier(priv);
 
 	return dev;
 }
@@ -3673,7 +3684,7 @@ void free_orinocodev(struct net_device *dev)
 		kfree(rx_data);
 	}
 
-	unregister_pm_notifier(&priv->pm_notifier);
+	orinoco_unregister_pm_notifier(priv);
 	orinoco_uncache_fw(priv);
 
 	priv->wpa_ie_len = 0;