io_uring/kbuf: check for ring provided buffers first in recycling

This is the most likely of paths if a provided buffer is used, so offer
it up first and push the legacy buffers to later.

Link: https://lore.kernel.org/r/20250821020750.598432-14-axboe@kernel.dk


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