block: remove a pointless call to MINOR() in device_add_disk

blk_alloc_ext_minor already returns just a minor number, so no need to
mask the high bits.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210824075216.1179406-2-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>