MAINTAINERS: Add `include/linux/io_uring_types.h`

File include/linux/io_uring_types.h doesn't have a maintainer, add it
to the io_uring section.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>