clear additional flags on erase to prevent errors

Author: chrissnow

targets/TARGET_STM/TARGET_STM32L1/flash_api.c

@@ -50,9 +50,7 @@ int32_t flash_erase_sector(flash_t *obj, uint32_t address)
         return -1;
     }
 
-    /* Clear OPTVERR bit set on virgin samples */
-    __HAL_FLASH_CLEAR_FLAG(FLASH_FLAG_OPTVERR);
-
+	__HAL_FLASH_CLEAR_FLAG(FLASH_FLAG_EOP | FLASH_FLAG_PGAERR | FLASH_FLAG_WRPERR);
     /* MBED HAL erases 1 sector at a time */
     /* Fill EraseInit structure*/
     EraseInitStruct.TypeErase   = FLASH_TYPEERASE_PAGES;