io_uring/rsrc: rename rsrc_list

We have too many "rsrc" around which makes the name of struct
io_rsrc_node::rsrc_list confusing. The field is responsible for keeping
a list of files or buffers, so call it item_list and add comments
around.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3e34d4dfc1fdbb6b520f904ee6187c2ccf680efe.1680576071.git.asml.silence@gmail.com


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