[MLIR] Fix documentation of the ExecutionEngine in the toy tutorial example

Differential Revision: https://reviews.llvm.org/D105813

Author: frgossen

mlir/docs/Tutorials/Toy/Ch-6.md

@@ -293,7 +293,8 @@ int runJit(mlir::ModuleOp module) {
 
   // Create an MLIR execution engine. The execution engine eagerly JIT-compiles
   // the module.
-  auto maybeEngine = mlir::ExecutionEngine::create(module, optPipeline);
+  auto maybeEngine = mlir::ExecutionEngine::create(module,
+      /*llvmModuleBuilder=*/nullptr, optPipeline);
   assert(maybeEngine && "failed to construct an execution engine");
   auto &engine = maybeEngine.get();