io_uring/rsrc: use nospec'ed indexes

We use array_index_nospec() for registered buffer indexes, but don't use
it while poking into rsrc tags, fix that.

Fixes: 634d00df

 ("io_uring: add full-fledged dynamic buffers support")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f02fafc5a9c0dd69be2b0618c38831c078232ff0.1681395792.git.asml.silence@gmail.com


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