tests/kernel/sched/schedule_api: don't break the test if not divisible

When test tests/kernel/sched/schedule_api, it shows "ASSERTION FAIL:
timeslice in ticks much be divisible by two", then break and fail
the test.

Fixes #44887.

On board it8xxx2_evb, it can pass schedule_api test without
the assertion, so I add the floating part back to half_slice_cyc
when the timeslice in ticks can't be divisible by two.
After change, the time slice will be:
1.slice_ticks = (200x8192+999)/1000 = 1639 (not changed)
2.before add the deviation (not handle the floating part):
half_slice_cyc = (1639/2) * (32768/8192) = (819) * (32768/8192) = 3276,
after add the deviation:
half_slice_cyc = 3276 + (32768/8192/2) = 3278,
and it's equal (1639/2) * (32768/8192) = 3278.

Verified by test pattern:
west build -p always -b it8xxx2_evb tests/kernel/sched/schedule_api

Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>
1 file changed