f2fs: remove the redundant variable definition

The variable 'i' has been defined before, so here we can
use it directly.

Signed-off-by: Kaixu Xia <xiakaixu@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1163,7 +1163,6 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	/* write nat bits */
 	if (enabled_nat_bits(sbi, cpc)) {
 		__u64 cp_ver = cur_cp_version(ckpt);
-		unsigned int i;
 		block_t blk;
 
 		cp_ver |= ((__u64)crc32 << 32);