Fix multiple servos with STM32 (#16151)

Marlin/src/HAL/HAL_STM32/Servo.h

@@ -27,11 +27,13 @@
 // Inherit and expand on the official library
 class libServo : public Servo {
   public:
+    libServo();
     int8_t attach(const int pin);
     int8_t attach(const int pin, const int min, const int max);
     void move(const int value);
   private:
     typedef Servo super;
-    uint16_t min_ticks, max_ticks;
-    uint8_t servoIndex;               // index into the channel data for this servo
+
+    int servo_pin = 0;
+    millis_t delay = 0;
 };