mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write

memcg_path_store() assigns a newly allocated memory buffer to filter->memcg_path, without deallocating the previously allocated and assigned memory buffer. As a result, users can leak kernel memory by continuously writing a data to memcg_path DAMOS sysfs file. Fix the leak by deallocating the previously set memory buffer.