art: fix dlopen error message

detail is a std::string *, dereference it when logging the error
message.

Change-Id: If73a5806445df17d91ff1a7f4f3a6d31f0e9f54e
diff --git a/runtime/jni_internal.cc b/runtime/jni_internal.cc
index 38aeaee..c04aabf 100644
--- a/runtime/jni_internal.cc
+++ b/runtime/jni_internal.cc
@@ -3143,7 +3143,7 @@
 
   if (handle == nullptr) {
     *detail = dlerror();
-    LOG(ERROR) << "dlopen(\"" << path << "\", RTLD_LAZY) failed: " << detail;
+    LOG(ERROR) << "dlopen(\"" << path << "\", RTLD_LAZY) failed: " << *detail;
     return false;
   }