ublk: fix ublk_ch_mmap() for 64K page size

ublk: fix ublk_ch_mmap() for 64K page size

In ublk_ch_mmap(), queue id is calculated in the following way:

	(vma->vm_pgoff << PAGE_SHIFT) / `max_cmd_buf_size`

'max_cmd_buf_size' is equal to

	`UBLK_MAX_QUEUE_DEPTH * sizeof(struct ublksrv_io_desc)`

and UBLK_MAX_QUEUE_DEPTH is 4096 and part of UAPI, so 'max_cmd_buf_size'
is always page aligned in 4K page size kernel. However, it isn't true in
64K page size kernel.

Fixes the issue by always rounding up 'max_cmd_buf_size' with PAGE_SIZE.

Cc: stable@vger.kernel.org
Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20241111110718.1394001-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>