xen/blkfront: fix bug in backported patch

The backport of commit 8f5a695 ("xen/blkfront: don't take local
copy of a request from the ring page") to stable 4.4 kernel introduced
a bug when adding the needed blkif_ring_get_request() function, as
info->ring.req_prod_pvt was incremented twice now.

Fix that be deleting the now superfluous increments after calling that
function.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/block/xen-blkfront.c

@@ -493,8 +493,6 @@ static int blkif_queue_discard_req(struct request *req)
 	else
 		ring_req->u.discard.flag = 0;
 
-	info->ring.req_prod_pvt++;
-
 	/* Copy the request to the ring page. */
 	*final_ring_req = *ring_req;
 	info->shadow[id].inflight = true;
@@ -711,8 +709,6 @@ static int blkif_queue_rw_req(struct request *req)
 	if (setup.segments)
 		kunmap_atomic(setup.segments);
 
-	info->ring.req_prod_pvt++;
-
 	/* Copy request(s) to the ring page. */
 	*final_ring_req = *ring_req;
 	info->shadow[id].inflight = true;