[mlir][linalg] Fix `FoldInitTensorWithDimOp` if dim(init_tensor) is static.

[pifon2a]

Summary

It looks like it was a typo. Instead of *maybeConstantIndex,
initTensorOp.getStaticSize(*maybeConstantIndex) should be used to access the
dim size of the tensor. There is a test for that in canonicalize.mlir, but it
was working correctly because ReplaceStaticShapeDims was canonicalizing DimOp
before FoldInitTensorWithDimOp. So, to make the patterns more "orthogonal",
this case is disabled.

mlir/lib/Dialect/Linalg/IR/LinalgOps.cpp

struct FoldInitTensorWithDimOp : public OpRewritePattern<tensor::DimOp> {
   using OpRewritePattern<tensor::DimOp>::OpRewritePattern;
 
   LogicalResult matchAndRewrite(tensor::DimOp dimOp,
                                 PatternRewriter &rewriter) const override {
     Optional<int64_t> maybeConstantIndex = dimOp.getConstantIndex();
     auto initTensorOp = dimOp.source().getDefiningOp<linalg::InitTensorOp>();
     if (!initTensorOp || !maybeConstantIndex)
       return failure();
-    if (initTensorOp.isDynamicSize(*maybeConstantIndex)) {
-      rewriter.replaceOp(dimOp,
-                         initTensorOp.getDynamicSize(*maybeConstantIndex));
-      return success();
-    }
-    rewriter.replaceOpWithNewOp<ConstantIndexOp>(dimOp, *maybeConstantIndex);
+    if (!initTensorOp.isDynamicSize(*maybeConstantIndex))
+      return failure();
+    rewriter.replaceOp(dimOp, initTensorOp.getDynamicSize(*maybeConstantIndex));
     return success();
   }
 };
 } // namespace
 
 void InitTensorOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                MLIRContext *context) {
   results.add<FoldInitTensorWithDimOp, FoldInitTensorWithExtractSliceOp,