tests/kernel/timer/timer_api: modify logic for longer real time

SYS_CLOCK_TICKS_PER_SEC of it8xxx2 is 4096 (244us).
Running test_sleep_abs item on it8xxx2 and we get
k_us_to_ticks_ceil32(250) = 2 and late = 2, so it failed.
After we enable the CONFIG_PM, it needs more time to resume
from low power mode, so I modify the logic to <= for passing
the test.

fixes #49605

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