[mlir][sparse] fix unused variable warning on release build (#68824)

Author: PeimingLiu

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorCodegen.cpp

@@ -710,6 +710,8 @@ struct SparseSortCOOConverter : public OpConversionPattern<ConvertOp> {
 
     // Otherwise we need another data shuffle and a non-identity map.
     assert(dstStt.hasSameDimToLvl(srcStt));
+    (void)dstStt; // to silence warning when assertion is disabled
+
     auto id = AffineMap::getMultiDimIdentityMap(srcStt.getLvlRank(), ctx);
 
     rewriter.create<SortOp>(loc, nnz, crd, ValueRange{val}, id,

mlir/lib/Dialect/SparseTensor/Transforms/StageSparseOperations.cpp

@@ -36,6 +36,8 @@ struct StageUnorderedConvert : public OpRewritePattern<ConvertOp> {
     // source -> coo
     // The tmp COO must be unordered, otherwise it is a direct conversion.
     assert(!(srcStt.hasSameDimToLvl(dstStt) && srcStt.isAllOrdered()));
+    (void)srcStt; // to silence warning when assertion is disabled
+
     Type srcCOOTp = getCOOFromTypeWithOrdering(
         dstStt.getRankedTensorType(), dstStt.getDimToLvl(), /*ordered=*/false);
     Value srcCOO = rewriter.create<ConvertOp>(loc, srcCOOTp, op.getSource());