fix (#3286)

Author: BarclayII

src/array/cuda/cuda_filter.cu

@@ -10,11 +10,11 @@
 #include "../../runtime/cuda/cuda_hashtable.cuh"
 #include "./dgl_cub.cuh"
 
+using namespace dgl::runtime::cuda;
+
 namespace dgl {
 namespace array {
 
-using namespace dgl::runtime::cuda;
-
 namespace {
 
 // TODO(nv-dlasalle): Replace with getting the stream from the context