f2fs: fix the number of orphan inode blocks

cp_pack_start_sum is calculated in do_checkpoint and is equal to
cpu_to_le32(1 + cp_payload_blks + orphan_blocks). The number of
orphan inode blocks is take advantage of by recover_orphan_inodes
to readahead meta pages and recovery inodes. However, current codes
forget to reduce the number of cp payload blocks when calculate
the number of orphan inode blocks. This patch fix it.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>