drivers: rtc: stm32: narrow backup domain access window during interrupts

Change backup domain access gating in STM32 RTC interrupt handler
to only request access when RTC registers ar to be modified
instead of during the whole RTC interrupts service including
interrupt consumer callback execution.

Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>

drivers/rtc/rtc_ll_stm32.c

@@ -283,13 +283,13 @@ void rtc_stm32_isr(const struct device *dev)
 	struct rtc_stm32_alrm *p_rtc_alrm;
 	int id = 0;
 
-	stm32_backup_domain_enable_access();
-
 	for (id = 0; id < RTC_STM32_ALARMS_COUNT; id++) {
 		if (rtc_stm32_is_active_alarm(RTC, (uint16_t)id) != 0) {
+			stm32_backup_domain_enable_access();
 			LL_RTC_DisableWriteProtection(RTC);
 			rtc_stm32_clear_alarm_flag(RTC, (uint16_t)id);
 			LL_RTC_EnableWriteProtection(RTC);
+			stm32_backup_domain_disable_access();
 
 			if (id == RTC_STM32_ALRM_A) {
 				p_rtc_alrm = &(data->rtc_alrm_a);
@@ -305,8 +305,6 @@ void rtc_stm32_isr(const struct device *dev)
 		}
 	}
 
-	stm32_backup_domain_disable_access();
-
 	ll_func_exti_clear_rtc_alarm_flag(RTC_STM32_EXTI_LINE);
 }