kvm tools: remove unneeded check from disk code

We already know 'disk' is non-null.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

disk/core.c

@@ -105,7 +105,7 @@ struct disk_image *disk_image__new(int fd, u64 size,
 	}
 
 #ifdef CONFIG_HAS_AIO
-	if (disk) {
+	{
 		pthread_t thread;
 
 		disk->evt = eventfd(0, 0);