block: fix overflow in blk_ioctl_discard()

There is no check for overflow of 'start + len' in blk_ioctl_discard().
Hung task occurs if submit an discard ioctl with the following param:
  start = 0x80000000000ff000, len = 0x8000000000fff000;
Add the overflow validation now.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240329012319.2034550-1-linan666@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>