Fix vold's use of readdir_r(3).

Change-Id: I805a1799755429dd1f6f3bdc2e6a02f483587b35
diff --git a/VolumeManager.cpp b/VolumeManager.cpp
index 957d06b..bdc7739 100644
--- a/VolumeManager.cpp
+++ b/VolumeManager.cpp
@@ -1471,7 +1471,7 @@
     }
 
     size_t dirent_len = offsetof(struct dirent, d_name) +
-            pathconf(directory, _PC_NAME_MAX) + 1;
+            fpathconf(dirfd(d), _PC_NAME_MAX) + 1;
 
     struct dirent *dent = (struct dirent *) malloc(dirent_len);
     if (dent == NULL) {