netback: remove redundant assignment

New value for netbk->mmap_pages[pending_idx] is assigned in
xen_netbk_alloc_page(), no need for a second assignment which
exposes internal to the outside world.
Signed-off-by: NWei Liu <wei.liu2@citrix.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/netback.c

@@ -940,8 +940,6 @@ static struct gnttab_copy *xen_netbk_get_requests(struct xen_netbk *netbk,
 		if (!page)
 			return NULL;
 
-		netbk->mmap_pages[pending_idx] = page;
-
 		gop->source.u.ref = txp->gref;
 		gop->source.domid = vif->domid;
 		gop->source.offset = txp->offset;
@@ -1336,8 +1334,6 @@ static unsigned xen_netbk_tx_build_gops(struct xen_netbk *netbk)
 			continue;
 		}
 
-		netbk->mmap_pages[pending_idx] = page;
-
 		gop->source.u.ref = txreq.gref;
 		gop->source.domid = vif->domid;
 		gop->source.offset = txreq.offset;