Fix SWITCHING_NOZZLE compile error (#11657)

Marlin/src/module/tool_change.cpp

             parking_extruder_tool_change(tmp_extruder, no_move);
           #endif
 
+          const float xdiff = hotend_offset[X_AXIS][tmp_extruder] - hotend_offset[X_AXIS][active_extruder],
+                      ydiff = hotend_offset[Y_AXIS][tmp_extruder] - hotend_offset[Y_AXIS][active_extruder],
+                      zdiff = hotend_offset[Z_AXIS][tmp_extruder] - hotend_offset[Z_AXIS][active_extruder];
+
           #if ENABLED(SWITCHING_NOZZLE)
             // Always raise by at least 1 to avoid workpiece
-            const float zdiff = hotend_offset[Z_AXIS][active_extruder] - hotend_offset[Z_AXIS][tmp_extruder];
-            current_position[Z_AXIS] += (zdiff > 0.0 ? zdiff : 0.0) + 1;
+            current_position[Z_AXIS] += (zdiff < 0.0 ? -zdiff : 0.0) + 1;
             planner.buffer_line_kinematic(current_position, planner.max_feedrate_mm_s[Z_AXIS], active_extruder);
             move_nozzle_servo(tmp_extruder);
           #endif
 
-          const float xdiff = hotend_offset[X_AXIS][tmp_extruder] - hotend_offset[X_AXIS][active_extruder],
-                      ydiff = hotend_offset[Y_AXIS][tmp_extruder] - hotend_offset[Y_AXIS][active_extruder],
-                      zdiff = hotend_offset[Z_AXIS][tmp_extruder] - hotend_offset[Z_AXIS][active_extruder];
-
           #if ENABLED(DEBUG_LEVELING_FEATURE)
             if (DEBUGGING(LEVELING)) {
               SERIAL_ECHOPAIR("Offset Tool XY by { ", xdiff);