Disk io library: add missing const qualifier to doubly linked list accessors.
Disk io library: add missing const qualifier to doubly linked list accessors.

quantcast/qfs,thebigbrain/qfs,fengshao0907/qfs,quantcast/qfs,qnu/qfs,chanwit/qfs,quantcast/qfs,quantcast/qfs,fengshao0907/qfs,qnu/qfs,quantcast/qfs,chanwit/qfs,qnu/qfs,chanwit/qfs,quantcast/qfs,fengshao0907/qfs,thebigbrain/qfs,fengshao0907/qfs,qnu/qfs,chanwit/qfs,thebigbrain/qfs,quantcast/qfs,chanwit/qfs,fengshao0907/qfs,fengshao0907/qfs,qnu/qfs,thebigbrain/qfs,fengshao0907/qfs,thebigbrain/qfs,qnu/qfs,thebigbrain/qfs,fengshao0907/qfs,qnu/qfs,chanwit/qfs,thebigbrain/qfs,thebigbrain/qfs,chanwit/qfs,qnu/qfs,chanwit/qfs,quantcast/qfs