Fix for Stepper::set_directions() compilation error (#11838)

Marlin/src/module/stepper.h

@@ -466,14 +466,13 @@ class Stepper {
       #endif
     }
 
-  private:
+    // Set direction bits for all steppers
+    static void set_directions();
 
+  private:
     // Set the current position in steps
     static void _set_position(const int32_t &a, const int32_t &b, const int32_t &c, const int32_t &e);
 
-    // Set direction bits for all steppers
-    static void set_directions();
-
     FORCE_INLINE static uint32_t calc_timer_interval(uint32_t step_rate, uint8_t scale, uint8_t* loops) {
       uint32_t timer;