block: move capacity from disk to part0

Move disk->capacity to part0->nr_sects and convert all users who
directly accessed the field to use {get|set}_capacity().  This is done
early to allow the __dev field to be moved.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/partitions/check.c

@@ -586,7 +586,7 @@ void del_gendisk(struct gendisk *disk)
 	disk_part_iter_exit(&piter);
 
 	invalidate_partition(disk, 0);
-	disk->capacity = 0;
+	set_capacity(disk, 0);
 	disk->flags &= ~GENHD_FL_UP;
 	unlink_gendisk(disk);
 	disk_stat_set_all(disk, 0);