tool: make a few char pointers point to const char instead

These are read-only.

Closes https://github.com/curl/curl/pull/4771

src/tool_getparam.c

@@ -1985,8 +1985,7 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
       }
       {
         /* byte range requested */
-        char *tmp_range;
-        tmp_range = nextarg;
+        const char *tmp_range = nextarg;
         while(*tmp_range != '\0') {
           if(!ISDIGIT(*tmp_range) && *tmp_range != '-' && *tmp_range != ',') {
             warnf(global, "Invalid character is found in given range. "

src/tool_paramhlp.c

@@ -560,7 +560,7 @@ int ftpcccmethod(struct OperationConfig *config, const char *str)
   return CURLFTPSSL_CCC_PASSIVE;
 }
 
-long delegation(struct OperationConfig *config, char *str)
+long delegation(struct OperationConfig *config, const char *str)
 {
   if(curl_strequal("none", str))
     return CURLGSSAPI_DELEGATION_NONE;

src/tool_paramhlp.h

@@ -50,7 +50,7 @@ int ftpfilemethod(struct OperationConfig *config, const char *str);
 
 int ftpcccmethod(struct OperationConfig *config, const char *str);
 
-long delegation(struct OperationConfig *config, char *str);
+long delegation(struct OperationConfig *config, const char *str);
 
 ParameterError str2tls_max(long *val, const char *str);