Fix gcode_G26 error return

Marlin/G26_Mesh_Validation_Tool.cpp

       g26_bed_temp = parser.value_celsius();
       if (!WITHIN(g26_bed_temp, 15, 140)) {
         SERIAL_PROTOCOLLNPGM("?Specified bed temperature not plausible.");
-        return G26_ERR;
+        return;
       }
     }
 
       g26_layer_height = parser.value_linear_units();
       if (!WITHIN(g26_layer_height, 0.0, 2.0)) {
         SERIAL_PROTOCOLLNPGM("?Specified layer height not plausible.");
-        return G26_ERR;
+        return;
       }
     }
 
         g26_retraction_multiplier = parser.value_float();
         if (!WITHIN(g26_retraction_multiplier, 0.05, 15.0)) {
           SERIAL_PROTOCOLLNPGM("?Specified Retraction Multiplier not plausible.");
-          return G26_ERR;
+          return;
         }
       }
       else {
         SERIAL_PROTOCOLLNPGM("?Retraction Multiplier must be specified.");
-        return G26_ERR;
+        return;
       }
     }
 
       g26_nozzle = parser.value_float();
       if (!WITHIN(g26_nozzle, 0.1, 1.0)) {
         SERIAL_PROTOCOLLNPGM("?Specified nozzle size not plausible.");
-        return G26_ERR;
+        return;
       }
     }
 
           g26_prime_flag = -1;
         #else
           SERIAL_PROTOCOLLNPGM("?Prime length must be specified when not using an LCD.");
-          return G26_ERR;
+          return;
         #endif
       }
       else {
         g26_prime_length = parser.value_linear_units();
         if (!WITHIN(g26_prime_length, 0.0, 25.0)) {
           SERIAL_PROTOCOLLNPGM("?Specified prime length not plausible.");
-          return G26_ERR;
+          return;
         }
       }
     }
       g26_filament_diameter = parser.value_linear_units();
       if (!WITHIN(g26_filament_diameter, 1.0, 4.0)) {
         SERIAL_PROTOCOLLNPGM("?Specified filament size not plausible.");
-        return G26_ERR;
+        return;
       }
     }
     g26_extrusion_multiplier *= sq(1.75) / sq(g26_filament_diameter); // If we aren't using 1.75mm filament, we need to
       g26_hotend_temp = parser.value_celsius();
       if (!WITHIN(g26_hotend_temp, 165, 280)) {
         SERIAL_PROTOCOLLNPGM("?Specified nozzle temperature not plausible.");
-        return G26_ERR;
+        return;
       }
     }
 
     #else
       if (!parser.seen('R')) {
         SERIAL_PROTOCOLLNPGM("?(R)epeat must be specified when not using an LCD.");
-        return G26_ERR;
+        return;
       }
       else
         g26_repeats = parser.has_value() ? parser.value_int() : GRID_MAX_POINTS + 1;
     #endif
     if (g26_repeats < 1) {
       SERIAL_PROTOCOLLNPGM("?(R)epeat value not plausible; must be at least 1.");
-      return G26_ERR;
+      return;
     }
 
     g26_x_pos = parser.seenval('X') ? RAW_X_POSITION(parser.value_linear_units()) : current_position[X_AXIS];
     g26_y_pos = parser.seenval('Y') ? RAW_Y_POSITION(parser.value_linear_units()) : current_position[Y_AXIS];
     if (!position_is_reachable(g26_x_pos, g26_y_pos)) {
       SERIAL_PROTOCOLLNPGM("?Specified X,Y coordinate out of bounds.");
-      return G26_ERR;
+      return;
     }
 
     /**