NFSv2: Fix write regression

[ Upstream commit d33d4beb522987d1c305c12500796f9be3687dee ]

Ensure we update the write result count on success, since the
RPC call itself does not do so.
Reported-by: NJan Stancek <jstancek@redhat.com>
Reported-by: NNaresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>
Tested-by: NJan Stancek <jstancek@redhat.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>

fs/nfs/proc.c

@@ -616,8 +616,10 @@ static int nfs_proc_pgio_rpc_prepare(struct rpc_task *task,
 
 static int nfs_write_done(struct rpc_task *task, struct nfs_pgio_header *hdr)
 {
-	if (task->tk_status >= 0)
+	if (task->tk_status >= 0) {
+		hdr->res.count = hdr->args.count;
 		nfs_writeback_update_inode(hdr);
+	}
 	return 0;
 }