tests: portability: cmsis_rtos_v1: Increase clock tolerance

Increased accepted difference between system clock and
k_busy_wait clock. Some platforms (e.g. Nordic SoC) are using
different clocks for system clock (low frequency) and k_busy_wait
(high frequency). If those clocks are driven from low accuracy
source like RC oscillator then difference may be significant.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>