STM32 RTC : skip rtc_write if possible

Author: jeromecoutant

targets/TARGET_STM/rtc_api.c

@@ -207,6 +207,11 @@ void rtc_write(time_t t)
     RTC_DateTypeDef dateStruct = {0};
     RTC_TimeTypeDef timeStruct = {0};
 
+    /* if the requested time is the current time, no need to continue */
+    if (t == rtc_read()) {
+        return;
+    }
+
     core_util_critical_section_enter();
     RtcHandle.Instance = RTC;