Fix kernel-doc to match the function's changed args.

Warning(fs/fs-writeback.c:190): No description found for parameter 'args'
Warning(fs/fs-writeback.c:190): Excess function parameter 'sb' description in 'bdi_queue_work_onstack'
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>