core: fix HardwareSerial compilation failed when USART disabled#1697

fpistm merged 1 commit intostm32duino:mainstm32duino/Arduino_Core_STM32:mainfrom

ABOSTM:HARDWARESERIAL_DISABLED_FAILEDABOSTM/Arduino_Core_STM32:HARDWARESERIAL_DISABLED_FAILEDCopy head branch name to clipboard