Pass the std:min argument's type, to avoid the compilation error. (#3637)

* Pass the std:min argument's type, to avoid the compilation error.

* Update parallel_for.h

* Update negative_sampling.cc
Co-authored-by: Quan (Andy) Gan <coin2028@hotmail.com>

include/dgl/runtime/parallel_for.h

@@ -165,7 +165,7 @@ DType parallel_reduce(
     auto chunk_size = divup((end - begin), num_threads);
     auto begin_tid = begin + tid * chunk_size;
     if (begin_tid < end) {
-      auto end_tid = std::min(end, chunk_size + begin_tid);
+      auto end_tid = std::min(end, static_cast<size_t>(chunk_size + begin_tid));
       try {
         results[tid] = f(begin_tid, end_tid, ident);
       } catch (...) {

src/array/cpu/negative_sampling.cc

@@ -57,7 +57,7 @@ std::pair<IdArray, IdArray> CSRGlobalUniformNegativeSampling(
         });;
     end = std::unique(begin, end);
   }
-  int64_t num_sampled = std::min(end - begin, num_samples);
+  int64_t num_sampled = std::min(static_cast<int64_t>(end - begin), num_samples);
   return {row.CreateView({num_sampled}, row->dtype), col.CreateView({num_sampled}, col->dtype)};
 }