f2fs: set page private for inmemory pages for truncation

The inmemory pages should be handled by invalidate_page since it needs to be
released int the truncation path.
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -180,6 +180,8 @@ void register_inmem_page(struct inode *inode, struct page *page)
 	struct inmem_pages *new;
 	int err;
 
+	SetPagePrivate(page);
+
 	new = f2fs_kmem_cache_alloc(inmem_entry_slab, GFP_NOFS);
 
 	/* add atomic page indices to the list */