[Kernel] Use omp flush in CSRIsSorted (#1725)

* Use omp flush

* test

* test

* remove omp
Co-authored-by: Ubuntu <ubuntu@ip-172-31-51-214.ec2.internal>
Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>

src/array/cpu/csr_sort.cc

@@ -18,7 +18,7 @@ bool CSRIsSorted(CSRMatrix csr) {
   const IdType* indptr = csr.indptr.Ptr<IdType>();
   const IdType* indices = csr.indices.Ptr<IdType>();
   bool ret = true;
-#pragma omp parallel for shared(ret)
+
   for (int64_t row = 0; row < csr.num_rows; ++row) {
     if (!ret)
       continue;