virtio: Silence uninitialized variable warning

Smatch complains that we might not initialize "queue".  The issue is
callers like setup_vq() from virtio_pci_modern.c where "num" could be
something like 2 and "vring_align" is 64.  In that case, vring_size() is
less than PAGE_SIZE.  It won't happen in real life, but we're getting
the value of "num" from a register so it's not really possible to tell
what value it holds with static analysis.

Let's just silence the warning.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -1006,7 +1006,7 @@ struct virtqueue *vring_create_virtqueue(
 	const char *name)
 {
 	struct virtqueue *vq;
-	void *queue;
+	void *queue = NULL;
 	dma_addr_t dma_addr;
 	size_t queue_size_in_bytes;
 	struct vring vring;