windfarm: decrement client count when unregistering

wf_unregister_client() increments the client count when a client
unregisters. That is obviously incorrect. Decrement that client count
instead.

Fixes: 75722d39 ("[PATCH] ppc64: Thermal control for SMU based machines")
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/macintosh/windfarm_core.c

@@ -435,7 +435,7 @@ int wf_unregister_client(struct notifier_block *nb)
 {
 	mutex_lock(&wf_lock);
 	blocking_notifier_chain_unregister(&wf_client_list, nb);
-	wf_client_count++;
+	wf_client_count--;
 	if (wf_client_count == 0)
 		wf_stop_thread();
 	mutex_unlock(&wf_lock);