virtio: Fix virtio buffer allocation

Change-Id: I0ffb468aef56f5fd223218a83425771595863666
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
diff --git a/src/vnet/devices/virtio/pci.c b/src/vnet/devices/virtio/pci.c
index b02b79d..aeb519b 100644
--- a/src/vnet/devices/virtio/pci.c
+++ b/src/vnet/devices/virtio/pci.c
@@ -693,7 +693,7 @@
       do
 	{
 	  if (n_alloc < queue_size)
-	    n_alloc =
+	    n_alloc +=
 	      vlib_buffer_alloc (vm, vring->indirect_buffers + n_alloc,
 				 queue_size - n_alloc);
 	}