Fix steps_to_mm for active extruders

Marlin/planner.cpp

 void Planner::sync_from_steppers() {
   LOOP_XYZE(i) position[i] = stepper.position((AxisEnum)i);
   #if ENABLED(LIN_ADVANCE)
-    LOOP_XYZE(i) position_float[i] = stepper.position((AxisEnum)i) * steps_to_mm[i];
+    LOOP_XYZE(i) position_float[i] = stepper.position((AxisEnum)i) * (i == E_AXIS ? steps_to_mm[E_AXIS + active_extruder] : steps_to_mm[i]);
   #endif
 }