Fix the planeNormal calculation

Marlin/Marlin_main.cpp

@@ -1110,11 +1110,13 @@ static void set_bed_level_equation_3pts(float z_at_pt_1, float z_at_pt_2, float
     vector_3 pt1 = vector_3(ABL_PROBE_PT_1_X, ABL_PROBE_PT_1_Y, z_at_pt_1);
     vector_3 pt2 = vector_3(ABL_PROBE_PT_2_X, ABL_PROBE_PT_2_Y, z_at_pt_2);
     vector_3 pt3 = vector_3(ABL_PROBE_PT_3_X, ABL_PROBE_PT_3_Y, z_at_pt_3);
+    vector_3 planeNormal = vector_3::cross(pt1 - pt2, pt3 - pt2).get_normal();
 
-    vector_3 from_2_to_1 = (pt1 - pt2).get_normal();
-    vector_3 from_2_to_3 = (pt3 - pt2).get_normal();
-    vector_3 planeNormal = vector_3::cross(from_2_to_1, from_2_to_3).get_normal();
-    planeNormal = vector_3(planeNormal.x, planeNormal.y, planeNormal.z);
+    if (planeNormal.z < 0) {
+      planeNormal.x = -planeNormal.x;
+      planeNormal.y = -planeNormal.y;
+      planeNormal.z = -planeNormal.z;
+    }
 
     plan_bed_level_matrix = matrix_3x3::create_look_at(planeNormal);