md: raid5: add prerequisite to run underneath dm-raid

In case md runs underneath the dm-raid target, the mddev does not have
a request queue or gendisk, thus avoid accesses.

This patch adds a missing conditional to the raid5 personality.

Signed-of-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5.c

@@ -7572,8 +7572,10 @@ static void raid5_finish_reshape(struct mddev *mddev)
 
 		if (mddev->delta_disks > 0) {
 			md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
-			set_capacity(mddev->gendisk, mddev->array_sectors);
-			revalidate_disk(mddev->gendisk);
+			if (mddev->queue) {
+				set_capacity(mddev->gendisk, mddev->array_sectors);
+				revalidate_disk(mddev->gendisk);
+			}
 		} else {
 			int d;
 			spin_lock_irq(&conf->device_lock);