add const in allocate_mixing_dmr

Author: WHUweiqingzhou

source/module_elecstate/module_charge/charge_mixing.h

@@ -56,7 +56,7 @@ class Charge_Mixing
      * @brief allocate memory of dmr_mdata
      * @param nnr size of real-space density matrix
      */
-    void allocate_mixing_dmr(int nnr);
+    void allocate_mixing_dmr(const int nnr);
 
     /**
      * @brief charge mixing

source/module_elecstate/module_charge/charge_mixing_dmr.cpp

@@ -3,7 +3,7 @@
 #include "module_parameter/parameter.h"
 #include "module_base/timer.h"
 
-void Charge_Mixing::allocate_mixing_dmr(int nnr)
+void Charge_Mixing::allocate_mixing_dmr(const int nnr)
 {
     // Note that: we cannot allocate memory for dmr_mdata in set_mixing.
     // since the size of dmr_mdata is given by the size of HContainer.nnr, which is calculated in DensityMatrix::init_DMR().