io_uring/rsrc: add last-lookup cache hit to io_rsrc_node_lookup()

io_uring/rsrc: add last-lookup cache hit to io_rsrc_node_lookup()

This avoids array_index_nospec() for repeated lookups on the same node,
which can be quite common (and costly). If a cached node is removed from
the given table, it'll get cleared in the cache as well.
io_reset_rsrc_node() takes care of that, which is used in the spots
that's replacing a node.

Note: need to double check this is 100% safe wrt speculation, but I
believe it should be as we're not using the passed in value to index
any arrays (directly).

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