Input: remove useless synchronize_rcu() calls

There is no need to call synchronize_rcu() after a list insertion,
or a NULL->ptr assignment.

However, the reverse operations do need this call.

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/evdev.c

···
 		return error;
 
 	rcu_assign_pointer(evdev->grab, client);
-	synchronize_rcu();
 
 	return 0;
 }
···
 	spin_lock(&evdev->client_lock);
 	list_add_tail_rcu(&client->node, &evdev->client_list);
 	spin_unlock(&evdev->client_lock);
-	synchronize_rcu();
 }
 
 static void evdev_detach_client(struct evdev *evdev,

drivers/input/input.c

···
 	}
 
 	rcu_assign_pointer(dev->grab, handle);
-	synchronize_rcu();
 
  out:
 	mutex_unlock(&dev->mutex);

drivers/input/joydev.c

···
 	spin_lock(&joydev->client_lock);
 	list_add_tail_rcu(&client->node, &joydev->client_list);
 	spin_unlock(&joydev->client_lock);
-	synchronize_rcu();
 }
 
 static void joydev_detach_client(struct joydev *joydev,

drivers/input/mousedev.c

···
 	spin_lock(&mousedev->client_lock);
 	list_add_tail_rcu(&client->node, &mousedev->client_list);
 	spin_unlock(&mousedev->client_lock);
-	synchronize_rcu();
 }
 
 static void mousedev_detach_client(struct mousedev *mousedev,