ide-atapi: don't abuse rq->buffer

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>
diff --git a/drivers/ide/ide-tape.c b/drivers/ide/ide-tape.c
index 3a53e08..aadf53c 100644
--- a/drivers/ide/ide-tape.c
+++ b/drivers/ide/ide-tape.c
@@ -828,7 +828,7 @@
 		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;