fix: munmap_all release all buffer

kernel/fs/mmap.cpp

@@ -149,6 +149,9 @@ void fs_munmap_all(std::list<mmap_t *> &mmap_list) {
         uint8_t *data = mmap->data;
         size_t npage = mmap->npage;
         mmap_write(mmap);
+        for (auto it : mmap->buf) {
+            buf_release(it);
+        }
         mmap_allocator.destroy(mmap);
         mmap_list.pop_front();
         free_npage(pcb, (uintptr_t) data, npage);