Fix testcache.c to avoid modifying constant

tests/testcache.c

@@ -64,8 +64,10 @@ int main(int argc, char *argv[])
 
     if (info_buf)
     {
-        strtok(info_buf, "\r\n");
-        printf("Rig_info: '%s'\n", info_buf);
+	char *s = strdup(info_buf);
+        strtok(s, "\r\n");
+        printf("Rig_info: '%s'\n", s);
+	free(s);
     }
 
     vfo_t vfo;