io_uring: Allocate only necessary memory in io_probe

We write at most IORING_OP_LAST entries in the probe buffer, so we don't
need to allocate temporary space for more than that.  As a side effect,
we no longer can overflow "size".

Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/20240619020620.5301-3-krisman@suse.de


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