RTC: Fix counter value when CLEAR after STOP

If TASK_CLEAR was called after TASK_STOP the counter
value would not be cleared. Fix it.

Thanks to Lang Xie for the report.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

src/HW_models/NHW_RTC.c

@@ -534,6 +534,7 @@ static void nhw_rtc_TASKS_CLEAR(uint rtc) {
 
   /* Pre-scaler value is latched to an internal register on tasks START, CLEAR, and TRIGOVRFLW */
   nhw_rtc_st[rtc].PRESC = NRF_RTC_regs[rtc].PRESCALER;
+  nhw_rtc_st[rtc].counter_at_stop = 0;
   nhw_rtc_set_counter(rtc, 0);
 }