firmware: don't return CYCCNT contents as it is always zero anyway (cycle counter is disabled)

embed/firmware/mphalport.h

@@ -1,9 +1,8 @@
-#include STM32_HAL_H
 
 #include "lib/utils/interrupt_char.h"
 
 static inline mp_uint_t mp_hal_ticks_cpu(void) {
-    return DWT->CYCCNT;
+    return 0;
 }
 
 void mp_hal_set_vcp_iface(int iface_num);