[NUCLEO_F401RE] Add missing IT flag reset + update system clock variable

libraries/mbed/targets/cmsis/TARGET_STM/TARGET_NUCLEO_F401RE/hal_tick.c

@@ -42,6 +42,7 @@ void us_ticker_irq_handler(void);
 void timer_irq_handler(void) {
     // Channel 1 for mbed timeout
     if (__HAL_TIM_GET_ITSTATUS(&TimMasterHandle, TIM_IT_CC1) == SET) {
+        __HAL_TIM_CLEAR_IT(&TimMasterHandle, TIM_IT_CC1);
         us_ticker_irq_handler();
     }
 

libraries/mbed/targets/hal/TARGET_STM/TARGET_NUCLEO_F401RE/pwmout_api.c

@@ -238,6 +238,9 @@ void pwmout_period_us(pwmout_t* obj, int us) {
 
     __HAL_TIM_DISABLE(&TimHandle);
 
+    // Update the SystemCoreClock variable
+    SystemCoreClockUpdate();
+
     TimHandle.Init.Period        = us - 1;
     TimHandle.Init.Prescaler     = (uint16_t)(SystemCoreClock / 1000000) - 1; // 1 µs tick
     TimHandle.Init.ClockDivision = 0;