set_z parameters marked const

Marlin/mesh_bed_leveling.h

@@ -39,7 +39,7 @@
 
     static FORCE_INLINE float get_probe_x(int8_t i) { return MESH_MIN_X + (MESH_X_DIST) * i; }
     static FORCE_INLINE float get_probe_y(int8_t i) { return MESH_MIN_Y + (MESH_Y_DIST) * i; }
-    void set_z(int8_t px, int8_t py, float z) { z_values[py][px] = z; }
+    void set_z(const int8_t px, const int8_t py, const float z) { z_values[py][px] = z; }
 
     inline void zigzag(int8_t index, int8_t &px, int8_t &py) {
       px = index % (MESH_NUM_X_POINTS);