tests: cmsis_rtos_v2: adjust timer period to avoid starvation

Most boards run with 10 kHz ticks producing a period of 5 ms for 50
tick interval used in the timer periodic test.  On Nordic 50 ticks
corresponds to 1.5 ms which is too short to complete the TC_PRINT()
call within the handler, causing the periodic timer to starve the
osDelay that would turn off the timer.

Adjust the period to be at least 5 ms or 50 ticks to avoid this
problem while not breaking other platform with slower tick rates.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>