Fix up error message in installd::prepare_app_cache_dir

Fix log when actual_mode and target_mode of the app_cache_dir
mismatch.

Current log - Mismatched cache GID/mode at <path>: found 10021 but \
               expected 10021
New log - Mismatched cache GID/mode at <path>: found 10021/target_mode \
               but expected 10021/actual_mode

Test: make

Change-Id: I0f9041ed5d436ccf8265cbab3852ae8d1b17a74a
diff --git a/cmds/installd/utils.cpp b/cmds/installd/utils.cpp
index dd32ac6..d83f601 100644
--- a/cmds/installd/utils.cpp
+++ b/cmds/installd/utils.cpp
@@ -1068,7 +1068,7 @@
     } else {
         // Mismatched GID/mode is recoverable; fall through to update
         LOG(DEBUG) << "Mismatched cache GID/mode at " << path << ": found " << st.st_gid
-                << " but expected " << gid;
+                << "/" << actual_mode << " but expected " << gid << "/" << target_mode;
     }
 
     // Directory is owned correctly, but GID or mode mismatch means it's