[libc] Round up time for GPU nanosleep implementation (#81630)

Summary:
The GPU `nanosleep` tests would occasionally fail. This was due to the
fact that we used integer division to determine how many ticks we had to
sleep for. This would then truncate, leaving us with a value just
slightly below the requested value. This would then occasionally leave
us with a return value of `-1`. This patch just changes the code to
round up by 1 so we always sleep for at least the requested value.