Fixing vector add pattern that incorrectly returns success.

The pattern is returning success even if it does no work leading to pattern application running up to the max iteration count and failing.

Reviewed By: nicolasvasilache, mravishankar

Differential Revision: https://reviews.llvm.org/D109791

mlir/lib/Dialect/Vector/VectorOps.cpp

@@ -793,7 +793,7 @@ struct CanonicalizeContractAdd : public OpRewritePattern<AddOpType> {
     Value a = addOp->getOperand(0), b = addOp->getOperand(1);
     vector::ContractionOp contract = canonicalize(a, b);
     contract = contract ? contract : canonicalize(b, a);
-    return success();
+    return contract ? success() : failure();
   }
 };