CVE-2019-14196: nfs: fix unbounded memcpy with a failed length check at nfs_lookup_reply

This patch adds a check to rpc_pkt.u.reply.data at nfs_lookup_reply.

Signed-off-by: Cheng Liu <liucheng32@huawei.com>
Reported-by: Fermín Serna <fermin@semmle.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>