Update mis-named argument description of blk_mq_map_queue().  This patch
also updates description that argument to software queue percpu context.
Signed-off-by: NMinwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: NJohn Garry <john.garry@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>