io_uring/rsrc: add io_reset_rsrc_node() helper

io_uring/rsrc: add io_reset_rsrc_node() helper

Puts and reset an existing node in a slot, if one exists. Returns true
if a node was there, false if not. This helps cleanup some of the code
that does a lookup just to clear an existing node.

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