[mlir] Fix typo for unknown operation

mlir/lib/IR/AsmPrinter.cpp

void SSANameState::printValueID(Value value, bool printResultNo,
 
   if (resultNo && printResultNo)
     stream << '#' << *resultNo;
 }
 
 void SSANameState::printOperationID(Operation *op, raw_ostream &stream) const {
   auto it = operationIDs.find(op);
   if (it == operationIDs.end()) {
-    stream << "<<UNKOWN OPERATION>>";
+    stream << "<<UNKNOWN OPERATION>>";
   } else {
     stream << '%' << it->second;
   }
 }
 
 ArrayRef<int> SSANameState::getOpResultGroups(Operation *op) {
   auto it = opResultGroups.find(op);
   return it == opResultGroups.end() ? ArrayRef<int>() : it->second;