Impact: rq->buffer usage cleanup
ide-atapi uses rq->buffer as private opaque value for internal special
requests.  rq->special isn't used for these cases (the only case where
rq->special is used is for ide-tape rw requests).  Use rq->special
instead.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
        blk_rq_init(NULL, rq);
        rq->cmd_type = REQ_TYPE_SPECIAL;
        rq->cmd_flags |= REQ_PREEMPT;
-       rq->buffer = (char *)pc;
+       rq->special = (char *)pc;
        rq->rq_disk = disk;
 
        if (pc->req_xfer) {
 
        rq = blk_get_request(drive->queue, READ, __GFP_WAIT);
        rq->cmd_type = REQ_TYPE_SPECIAL;
-       rq->buffer = (char *)pc;
+       rq->special = (char *)pc;
 
        if (pc->req_xfer) {
                rq->data = pc->buf;
 
                pc = &floppy->queued_pc;
                idefloppy_create_rw_cmd(drive, pc, rq, (unsigned long)block);
        } else if (blk_special_request(rq)) {
-               pc = (struct ide_atapi_pc *) rq->buffer;
+               pc = (struct ide_atapi_pc *)rq->special;
        } else if (blk_pc_request(rq)) {
                pc = &floppy->queued_pc;
                idefloppy_blockpc_cmd(floppy, pc, rq);
 
                goto out;
        }
        if (rq->cmd[13] & REQ_IDETAPE_PC1) {
-               pc = (struct ide_atapi_pc *) rq->buffer;
+               pc = (struct ide_atapi_pc *)rq->special;
                rq->cmd[13] &= ~(REQ_IDETAPE_PC1);
                rq->cmd[13] |= REQ_IDETAPE_PC2;
                goto out;