io_uring: inline io_dismantle_req

io_dismantle_req() is hot, and not _too_ huge. Inline it, there are 3
call sites, which hopefully will turn into 2 in the future.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/bdd2dc30716cac270c2403e99bccd6286e4ae201.1631115443.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>