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>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index e094675..9de857f 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2231,7 +2231,7 @@
 		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;