counter: stm32 rtc: improve reading registers

Synchronize reading two separate registers. In some edge cases the read
registers could point different dates.

Signed-off-by: Dawid Niedzwiecki <dawidn@google.com>

drivers/counter/counter_ll_stm32_rtc.c

@@ -192,9 +192,19 @@ static uint32_t rtc_stm32_read(const struct device *dev)
 #endif
 	ARG_UNUSED(dev);
 
-	/* Read time and date registers */
-	rtc_time = LL_RTC_TIME_Get(RTC);
+	/* Read time and date registers. Make sure value of the previous register
+	 * hasn't been changed while reading the next one.
+	 */
 #if !defined(COUNTER_NO_DATE)
+	do {
+		rtc_date = LL_RTC_DATE_Get(RTC);
+
+		do {
+			rtc_time = LL_RTC_TIME_Get(RTC);
+		} while (rtc_time != LL_RTC_TIME_Get(RTC));
+
+	} while (rtc_date != LL_RTC_DATE_Get(RTC));
+#else
 	rtc_date = LL_RTC_DATE_Get(RTC);
 #endif