🐛 Fix STM32 FastPWM

Marlin/src/HAL/STM32/fast_pwm.cpp

@@ -74,6 +74,8 @@ void set_pwm_frequency(const pin_t pin, int f_desired) {
   PinName pin_name = digitalPinToPinName(pin);
   TIM_TypeDef *Instance = (TIM_TypeDef *)pinmap_peripheral(pin_name, PinMap_PWM); // Get HAL timer instance
 
+  const PinName pin_name = digitalPinToPinName(pin);
+  TIM_TypeDef * const Instance = (TIM_TypeDef *)pinmap_peripheral(pin_name, PinMap_PWM); // Get HAL timer instance
   uint32_t index = get_timer_index(Instance);
 
   // Protect used timers
@@ -83,11 +85,11 @@ void set_pwm_frequency(const pin_t pin, int f_desired) {
     #endif
   ) return;
 
-  if (HardwareTimer_Handle[index] == nullptr) // If frequency is set before duty we need to create a handle here. 
+  if (HardwareTimer_Handle[index] == nullptr) // If frequency is set before duty we need to create a handle here.
     HardwareTimer_Handle[index]->__this = new HardwareTimer((TIM_TypeDef *)pinmap_peripheral(pin_name, PinMap_PWM));
   HT = (HardwareTimer *)(HardwareTimer_Handle[index]->__this);
   timer_freq[index] = f_desired; // Save the last frequency so duty will not set the default for this timer number.
-  HT->setOverflow(f_desired, HERTZ_FORMAT);   
+  HT->setOverflow(f_desired, HERTZ_FORMAT);
 }
 
 #endif // HAL_STM32