f2fs: use list_for_each rather than list_for_each_safe, in remove_orphan_inode()

As we remove the target single node, so list_for_each is enought, in order to
clean up, we use list_for_each_entry instead.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>