🐛 Fix BACKLASH_COMPENSATION compile (#24072)

Followup to #23826

Marlin/src/feature/backlash.cpp

@@ -162,6 +162,7 @@ int32_t Backlash::get_applied_steps(const AxisEnum axis) {
 }
 
 class Backlash::StepAdjuster {
+  private:
     xyz_long_t applied_steps;
   public:
     StepAdjuster() {
@@ -173,6 +174,8 @@ public:
     }
 };
 
+#if ENABLED(BACKLASH_GCODE)
+
   void Backlash::set_correction_uint8(const uint8_t v) {
     StepAdjuster adjuster;
     correction = v;
@@ -190,6 +193,8 @@ void Backlash::set_distance_mm(const AxisEnum axis, const float v) {
     }
   #endif
 
+#endif
+
 #if ENABLED(MEASURE_BACKLASH_WHEN_PROBING)
 
   #include "../module/probe.h"