NFSv4.2: fix copy stateid copying for the async copy

This patch fixes Dan Carpenter's report that the static checker
found a problem where memcpy() was copying into too small of a buffer.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Fixes: e0639dc5 ("NFSD introduce async copy feature")
Signed-off-by: NOlga Kornievskaia <kolga@netapp.com>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Reviewed-by: NDai Ngo <dai.ngo@oracle.com>

fs/nfsd/nfs4proc.c

@@ -1541,8 +1541,8 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 		if (!nfs4_init_copy_state(nn, copy))
 			goto out_err;
 		refcount_set(&async_copy->refcount, 1);
-		memcpy(&copy->cp_res.cb_stateid, &copy->cp_stateid,
-			sizeof(copy->cp_stateid));
+		memcpy(&copy->cp_res.cb_stateid, &copy->cp_stateid.stid,
+			sizeof(copy->cp_res.cb_stateid));
 		dup_copy_fields(copy, async_copy);
 		async_copy->copy_task = kthread_create(nfsd4_do_async_copy,
 				async_copy, "%s", "copy thread");