block: open code blk_max_size_offset in blk_rq_get_max_sectors

blk_rq_get_max_sectors always uses q->limits.chunk_sectors as the
chunk_sectors argument, and already checks for max_sectors through the
call to blk_queue_get_max_sectors.  That means much of
blk_max_size_offset is not needed and open coding it simplifies the code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220614090934.570632-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>