dataplane: fix shadowed return value

Propagate the error return value from get_indirect().  This bug was
introduced in commit 4d684832 ("vring: create a common function to parse
descriptors").

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/virtio/dataplane/vring.c

@@ -376,7 +376,7 @@ int vring_pop(VirtIODevice *vdev, Vring *vring,
         barrier();
 
         if (desc.flags & VRING_DESC_F_INDIRECT) {
-            int ret = get_indirect(vring, elem, &desc);
+            ret = get_indirect(vring, elem, &desc);
             if (ret < 0) {
                 goto out;
             }