face/rib/tools: avoid deprecate Block::fromBuffer overloads

refs #2553

Change-Id: I32ea424ab7547f59fea2fca70ad6f41cd90bab58
diff --git a/tools/nfdc.cpp b/tools/nfdc.cpp
index 02fe28a..207d3ee 100644
--- a/tools/nfdc.cpp
+++ b/tools/nfdc.cpp
@@ -178,10 +178,11 @@
                                     const ndn::util::FaceUri& canonicalUri)
 {
   size_t offset = 0;
+  bool isOk = false;
   ndn::Block block;
-  bool ok = ndn::Block::fromBuffer(data, offset, block);
+  std::tie(isOk, block) = ndn::Block::fromBuffer(data, offset);
 
-  if (!ok) {
+  if (!isOk) {
     if (m_allowCreate) {
       startFaceCreate(canonicalUri);
     }