block: move policy from disk to part0

Move disk->policy to part0->policy.  Implement and use get_disk_ro().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
index f16bb46..03c2cb6 100644
--- a/drivers/ide/ide-cd.c
+++ b/drivers/ide/ide-cd.c
@@ -1113,7 +1113,7 @@
 
 	if (write) {
 		/* disk has become write protected */
-		if (cd->disk->policy) {
+		if (get_disk_ro(cd->disk)) {
 			cdrom_end_request(drive, 0);
 			return ide_stopped;
 		}
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index c3de311..5b91915 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -548,7 +548,7 @@
 	 */
 	param->open_count = dm_open_count(md);
 
-	if (disk->policy)
+	if (get_disk_ro(disk))
 		param->flags |= DM_READONLY_FLAG;
 
 	param->event_nr = dm_get_event_nr(md);