block: simplify blkdev_nr_zones

Simplify the arguments to blkdev_nr_zones by passing a gendisk instead
of the block_device and capacity.  This also removes the need for
__blkdev_nr_zones as all callers are outside the fast path and can
deal with the additional branch.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/ioctl.c b/block/ioctl.c
index 7ac8a66..5de98b9 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -512,7 +512,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 	case BLKGETZONESZ:
 		return put_uint(arg, bdev_zone_sectors(bdev));
 	case BLKGETNRZONES:
-		return put_uint(arg, blkdev_nr_zones(bdev));
+		return put_uint(arg, blkdev_nr_zones(bdev->bd_disk));
 	case HDIO_GETGEO:
 		return blkdev_getgeo(bdev, argp);
 	case BLKRAGET: