pNFS/flexfiles: Fix the reset of struct pgio_header when resending

hdr->good_bytes needs to be set to the length of the request, not
zero.

Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -774,7 +774,7 @@ static void ff_layout_reset_write(struct nfs_pgio_header *hdr, bool retry_pnfs)
 			nfs_direct_set_resched_writes(hdr->dreq);
 			/* fake unstable write to let common nfs resend pages */
 			hdr->verf.committed = NFS_UNSTABLE;
-			hdr->good_bytes = 0;
+			hdr->good_bytes = hdr->args.count;
 		}
 		return;
 	}