fix cppcheck

source/firmware/arch/stm32f4xx/syscalls.c

@@ -79,41 +79,29 @@ caddr_t _sbrk(int incr)
 
 int _close(int file)
 {
-    file = file; /* avoid warning */
     return -1;
 }
 
 int _fstat(int file, struct stat *st)
 {
-    file = file; /* avoid warning */
     st->st_mode = S_IFCHR;
     return 0;
 }
 
 int _isatty(int file)
 {
-    file = file; /* avoid warning */
     return 1;
 }
 
 int _lseek(int file, int ptr, int dir) {
-    file = file; /* avoid warning */
-    ptr = ptr; /* avoid warning */
-    dir = dir; /* avoid warning */
     return 0;
 }
 
 int _read(int file, char *ptr, int len)
 {
-    file = file; /* avoid warning */
-    ptr = ptr; /* avoid warning */
-    len = len; /* avoid warning */
     return 0;
 }
 
 int _write(int file, char *ptr, int len) {
-    int todo = todo;
-    file = file; /* avoid warning */
-//    USB_VCOM_Send(ptr, len);
     return len;
 }