staging: hv: Fix the WARN_ON condition in free_net_device()

In a previous commit, 7a09876, ASSERT was changed to WARN_ON, but
the condition wasn't updated. This patch fixed this error.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/hv/netvsc.c

@@ -95,7 +95,7 @@ static struct netvsc_device *alloc_net_device(struct hv_device *device)
 
 static void free_net_device(struct netvsc_device *device)
 {
-	WARN_ON(atomic_read(&device->refcnt) == 0);
+	WARN_ON(atomic_read(&device->refcnt) != 0);
 	device->dev->ext = NULL;
 	kfree(device);
 }