f2fs: fix compile warning in f2fs_destroy_node_manager()

fs/f2fs/node.c: In function ‘f2fs_destroy_node_manager’:
fs/f2fs/node.c:3390:1: warning: the frame size of 1048 bytes is larger than 1024 bytes [-Wframe-larger-than=]
 3390 | }

Merging below pointer arrays into common one, and reuse it by cast type.

struct nat_entry *natvec[NATVEC_SIZE];
struct nat_entry_set *setvec[SETVEC_SIZE];

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>