[Bug] dfs_v2版本下dfs_statfs接口退出时未释放临时变量fullpath的内存

### RT-Thread Version

master

### Hardware Type/Architectures

gd32

### Develop Toolchain

Microsoft VScode

### Describe the bug

临时变量fullpath的内存由dfs_normalize_path通过malloc或strdup申请，dfs_statfs函数退出时未释放

### Other additional context

_No response_