virtio_ring: Merge identical variables

The variables `total_sg` and `descs_used` have the same value. Replace
the few uses of `total_sg` with `descs_used` to simplify the situation.

Signed-off-by: Andrew Scull <ascull@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 7f1cbc5..a6922ce 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -20,17 +20,16 @@
 		  unsigned int out_sgs, unsigned int in_sgs)
 {
 	struct vring_desc *desc;
-	unsigned int total_sg = out_sgs + in_sgs;
-	unsigned int i, n, avail, descs_used, uninitialized_var(prev);
+	unsigned int descs_used = out_sgs + in_sgs;
+	unsigned int i, n, avail, uninitialized_var(prev);
 	int head;
 
-	WARN_ON(total_sg == 0);
+	WARN_ON(descs_used == 0);
 
 	head = vq->free_head;
 
 	desc = vq->vring.desc;
 	i = head;
-	descs_used = total_sg;
 
 	if (vq->num_free < descs_used) {
 		debug("Can't add buf len %i - avail = %i\n",