xen/netback: fix incorrect usage of RING_HAS_UNCONSUMED_REQUESTS()

Commit 6fac592c ("xen: update ring.h") missed to fix one use case
of RING_HAS_UNCONSUMED_REQUESTS().
Reported-by: Jan Beulich <jbeulich@suse.com>
Fixes: 6fac592c ("xen: update ring.h")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20220530113459.20124-1-jgross@suse.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/xen-netback/netback.c

@@ -828,7 +828,7 @@ static void xenvif_tx_build_gops(struct xenvif_queue *queue,
 			break;
 		}
 
-		work_to_do = RING_HAS_UNCONSUMED_REQUESTS(&queue->tx);
+		work_to_do = XEN_RING_NR_UNCONSUMED_REQUESTS(&queue->tx);
 		if (!work_to_do)
 			break;