f2fs: convert recover_orphan_inodes to void

The recover_orphan_inodes() returns no error all the time, so we don't need to
check its errors.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
[Jaegeuk Kim: add description]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>