Fix erase init struct for flash erase

Author: majcher

targets/TARGET_STM/TARGET_STM32G0/flash_api.c

@@ -57,6 +57,7 @@ int32_t flash_erase_sector(flash_t *obj, uint32_t address)
     /* MBED HAL erases 1 sector at a time */
     /* Fill EraseInit structure*/
     EraseInitStruct.TypeErase   = FLASH_TYPEERASE_PAGES;
+    EraseInitStruct.Banks       = FLASH_BANK_1;
     EraseInitStruct.Page        = (address & 0xFFFFF) / 2048; // page size = 2048
     EraseInitStruct.NbPages     = 1;