f2fs: fix wrong data structure when create slab

It used nat_entry_set when create slab for sit_entry_set.
Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -2231,7 +2231,7 @@ int __init create_segment_manager_caches(void)
 		goto fail;
 
 	sit_entry_set_slab = f2fs_kmem_cache_create("sit_entry_set",
-			sizeof(struct nat_entry_set));
+			sizeof(struct sit_entry_set));
 	if (!sit_entry_set_slab)
 		goto destory_discard_entry;