Fix Chiron typos, file nav

Marlin/src/lcd/extui/lib/anycubic_chiron/FileNavigator.cpp

   currentfolderdepth = 0;
   currentindex = 0;
   lastpanelindex = 0;
-  ZERO(currentfolderindex)
+  ZERO(currentfolderindex);
 
   // Start at root folder
   while (!filelist.isAtRootDir()) filelist.upDir();
   if (currentfolderdepth == 0)
     currentfoldername[0] = '\0';
   else {
-    const char *pos = strchr(currentfoldername, '/');
+    char * const pos = strchr(currentfoldername, '/');
     *(pos + 1) = '\0';
   }
 }

Marlin/src/lcd/extui/lib/anycubic_chiron/FileNavigator.h

 
 class FileNavigator {
   public:
+    FileNavigator();
     static void reset();
     static void getFiles(uint16_t, panel_type_t, uint8_t filesneeded=4);
     static void upDIR();

Marlin/src/lcd/extui/lib/anycubic_chiron/chiron_tft.cpp

 
 void ChironTFT::ProcessPanelRequest() {
   // Break these up into logical blocks // as its easier to navigate than one huge switch case!
-  const int8_t tpos = FindToken('A');
+  int8_t tpos = FindToken('A');
   // Panel request are 'A0' - 'A36'
   if (tpos != -1) {
     const int8_t req = atoi(&panel_command[tpos+1]);