codepos not used in gcode_M28()

Got:
Marlin_main.cpp:2567: warning: unused variable 'codepos'

Needs revision.
Don't now how this should look like.

Marlin/Marlin_main.cpp

    * M28: Start SD Write
    */
   inline void gcode_M28() {
-    char* codepos = strchr_pointer + 4;
+//    char* codepos = strchr_pointer + 4; // ??? not used ???
     char* starpos = strchr(strchr_pointer + 4, '*');
     if (starpos) {
       char* npos = strchr(cmdbuffer[bufindr], 'N');