t/io_uring: fix 32-bit build warnings

t/io_uring: fix 32-bit build warnings

Also change the type for offset to long long since that's what is
expected by io_prep_pread.

Latency measurement for t/io_uring is actually broken on 32-bit builds
because iocb->data and io_event->data are 32-bit void pointers. So it is
not possible to fit both fileno and clock_index in there.

On a 32-bit build with 4-byte longs, the following warnings appear:

t/io_uring.c: In function ‘prep_more_ios_aio’:
t/io_uring.c:666:44: error: left shift count >= width of type [-Werror=shift-count-overflow]
  666 |    data |= ((unsigned long) s->clock_index << 32);
      |                                            ^~
t/io_uring.c: In function ‘reap_events_aio’:
t/io_uring.c:688:27: error: right shift count >= width of type [-Werror=shift-count-overflow]
  688 |    int clock_index = data >> 32;
      |                           ^~

Explicitly specify 64-bit types to resolve these warnings.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>