Use ADL to find stream operator

include/ck/host_utility/io.hpp

@@ -24,18 +24,20 @@ std::ostream& operator<<(std::ostream& os, const std::array<T, N>& v)
     return os;
 }
 
+namespace ck {
 template <typename... Ts>
-std::ostream& operator<<(std::ostream& os, const ck::TensorDescriptor<Ts...>& desc)
+std::ostream& operator<<(std::ostream& os, const TensorDescriptor<Ts...>& desc)
 {
-    constexpr ck::index_t nDim = ck::remove_cvref_t<decltype(desc)>::GetNumOfDimension();
+    constexpr index_t nDim = remove_cvref_t<decltype(desc)>::GetNumOfDimension();
 
     os << "{";
 
-    ck::static_for<0, nDim - 1, 1>{}([&](auto i) { os << desc.GetLength(i) << ", "; });
+    static_for<0, nDim - 1, 1>{}([&](auto i) { os << desc.GetLength(i) << ", "; });
 
-    os << desc.GetLength(ck::Number<nDim - 1>{});
+    os << desc.GetLength(Number<nDim - 1>{});
 
     os << "}";
 
     return os;
 }
+} // namespace ck