t/io_uring: fix 64-bit cast on 32-bit archs

t/io_uring: fix 64-bit cast on 32-bit archs

gcc complains that:

t/io_uring.c: In function ‘init_io_pt’:
t/io_uring.c:618:52: error: left shift count >= width of type [-Werror=shift-count-overflow]
  618 |   sqe->user_data |= ((unsigned long)s->clock_index << 32);
      |                                                    ^~

we're shifting more than the size of the type. Cast to a 64-bit value
so that it'll work on 32-bit as well.

Fixes: 7d04588a7663 ("t/io_uring: add support for async-passthru")
Signed-off-by: Jens Axboe <axboe@kernel.dk>