f2fs: check the right return value of memory alloc function

This patch check the right return value of memory alloc function
Signed-off-by: NYunlei He <heyunlei@huawei.com>
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -2798,7 +2798,7 @@ static int init_free_nid_cache(struct f2fs_sb_info *sbi)
 	for (i = 0; i < nm_i->nat_blocks; i++) {
 		nm_i->free_nid_bitmap[i] = f2fs_kvzalloc(sbi,
 			f2fs_bitmap_size(NAT_ENTRY_PER_BLOCK), GFP_KERNEL);
-		if (!nm_i->free_nid_bitmap)
+		if (!nm_i->free_nid_bitmap[i])
 			return -ENOMEM;
 	}