io_uring: remove dead 'sqe' store

The kernel test robot correctly identifies that we store sqe twice,
remove the earlier one that is done before validating the index.

Fixes: f75d1183 ("io_uring: harder fdinfo sq/cq ring iterating")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>