[WasmFS] Ensure error codes are negative in the Node backend

See commit 48459c6 for details.

Author: kleisauke

system/lib/wasmfs/backends/node_backend.cpp

@@ -254,7 +254,7 @@ class NodeDirectory : public Directory {
     }
 
     auto childPath = getChildPath(name);
-    return _wasmfs_node_rename(fromPath.c_str(), childPath.c_str());
+    return -_wasmfs_node_rename(fromPath.c_str(), childPath.c_str());
   }
 
   ssize_t getNumEntries() override {