f2fs: don't mark compressed inode dirty during f2fs_iget()

- f2fs_iget
 - do_read_inode
  - set_inode_flag(, FI_COMPRESSED_FILE)
   - __mark_inode_dirty_flag(, true)

It's unnecessary, so let's just mark compressed inode dirty while
compressed inode conversion.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>