fix: enable peripheral bus clock when SRD domain is in DRUN

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

src/STM32RTC.cpp

@@ -915,6 +915,9 @@ void STM32RTC::setY2kEpoch(uint32_t ts)
 void STM32RTC::configForLowPower(Source_Clock source)
 {
 #if defined(HAL_PWR_MODULE_ENABLED)
+#ifdef __HAL_RCC_RTCAPB_CLKAM_ENABLE
+  __HAL_RCC_RTCAPB_CLKAM_ENABLE();
+#endif
   if (!_configured) {
     _clockSource = source;
     // Enable RTC