io_uring: unify fsize with def->work_flags

This one was missed in the earlier conversion, should be included like
any of the other IO identity flags. Make sure we restore to RLIM_INIFITY
when dropping the personality again.

Fixes: 98447d65

 ("io_uring: move io identity items into separate struct")
Signed-off-by: Jens Axboe <axboe@kernel.dk>