[mlir][scf] Fix typo in description of option of TestSCFForUtilsPass (NFC).

[ingomueller-net]

Trivial, non-functional change --> self-accepting.

mlir/test/lib/Dialect/SCF/TestSCFUtils.cpp

struct TestSCFForUtilsPass
   StringRef getArgument() const final { return "test-scf-for-utils"; }
   StringRef getDescription() const final { return "test scf.for utils"; }
   explicit TestSCFForUtilsPass() = default;
   TestSCFForUtilsPass(const TestSCFForUtilsPass &pass) : PassWrapper(pass) {}
 
   Option<bool> testReplaceWithNewYields{
       *this, "test-replace-with-new-yields",
       llvm::cl::desc("Test replacing a loop with a new loop that returns new "
-                     "additional yeild values"),
+                     "additional yield values"),
       llvm::cl::init(false)};
 
   void runOnOperation() override {
     func::FuncOp func = getOperation();
     SmallVector<scf::ForOp, 4> toErase;
 
     if (testReplaceWithNewYields) {
       func.walk([&](scf::ForOp forOp) {