improve debug for event

Change-Id: If6c0e25729d9964cbe5967833247a6d791d575a0

include/hcc_detail/hip_hcc.h

@@ -715,5 +715,12 @@ inline std::ostream & operator<<(std::ostream& os, const dim3& s)
     return os;
 }
 
+// Stream printf functions:
+inline std::ostream& operator<<(std::ostream& os, const hipEvent_t& e)
+{
+    os << "event:" << std::hex << static_cast<void*> (e);
+    return os;
+}
+
 
 #endif

include/hcc_detail/trace_helper.h

@@ -63,7 +63,9 @@ inline std::string ToString(T v)
 template <>
 inline std::string ToString(hipEvent_t v) 
 {
-    return ToString(&v);
+    std::ostringstream ss;
+    ss << v;
+    return ss.str();
 };