io_uring: simplify iovec freeing in io_clean_op()

We don't get REQ_F_NEED_CLEANUP for rw unless there is ->free_iovec set,
so remove the optimisation of NULL checking it inline, kfree() will take
care if that would ever be the case.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a233dc655d3d45bd4f69b73d55a61de46d914415.1623949695.git.asml.silence@gmail.com


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