NFSD: copy the whole verifier in nfsd_copy_write_verifier

Currently, we're only memcpy'ing the first __be32. Ensure we copy into
both words.

Fixes: 91d2e9b5 ("NFSD: Clean up the nfsd_net::nfssvc_boot field")
Reported-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfssvc.c

@@ -363,7 +363,7 @@ void nfsd_copy_write_verifier(__be32 verf[2], struct nfsd_net *nn)
 
 	do {
 		read_seqbegin_or_lock(&nn->writeverf_lock, &seq);
-		memcpy(verf, nn->writeverf, sizeof(*verf));
+		memcpy(verf, nn->writeverf, sizeof(nn->writeverf));
 	} while (need_seqretry(&nn->writeverf_lock, seq));
 	done_seqretry(&nn->writeverf_lock, seq);
 }