[mlir] Fix gcc-5 build in ViewOpGraph.cpp

Differential Revision: https://reviews.llvm.org/D107458

Author: matthias-springer

mlir/lib/Transforms/ViewOpGraph.cpp

@@ -120,7 +120,7 @@ class PrintOpPass : public ViewOpGraphPassBase<PrintOpPass> {
   void emitAttrList(raw_ostream &os, const AttributeMap &map) {
     os << "[";
     interleaveComma(map, os, [&](const auto &it) {
-      os << attrStmt(it.getKey(), it.getValue());
+      os << this->attrStmt(it.getKey(), it.getValue());
     });
     os << "]";
   }