Fix kernel-doc warning in blk-core.c:

Warning(..//block/blk-core.c:1549): No description found for parameter 'same_queue_rq'
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>