io_uring/rsrc: don't skip offset calculation

Don't optimise for requests with offset=0. Large registered buffers are
the preference and hence the user is likely to pass an offset, and the
adjustments are not expensive and will be made even cheaper in following
patches.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1c2beb20470ee3c886a363d4d8340d3790db19f3.1744882081.git.asml.silence@gmail.com


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