fix: nucleo-l152RE: add missing clock configuration for ADC

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

Author: fpistm

variants/STM32L1xx/L151RET_L152RET_L162RET/variant_NUCLEO_L152RE.cpp

@@ -119,8 +119,10 @@ WEAK void SystemClock_Config(void)
    * Initializes the RCC Oscillators according to the specified parameters
    * in the RCC_OscInitTypeDef structure.
    */
-  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
+  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI | RCC_OSCILLATORTYPE_HSE;
   RCC_OscInitStruct.HSEState = RCC_HSE_BYPASS;
+  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
+  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
   RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
   RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
   RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL12;