Update VolumeManager to use UnmountTreeWithPrefix.

Bug: 122905493
Test: manual
Change-Id: Ia6aa1d400277a76dfd2c1db87c613d7e692b0b5c
diff --git a/Utils.cpp b/Utils.cpp
index 667d277..341c927 100644
--- a/Utils.cpp
+++ b/Utils.cpp
@@ -811,7 +811,7 @@
         return -errno;
     }
 
-    status_t result;
+    status_t result = OK;
     struct dirent* de;
     while ((de = readdir(dir))) {
         const char* name = de->d_name;