Bug fix:The CRC detection on px4io was failing with -1 result, do the…

… the fact that the PX4IO_Uploader had closed the port and Nuttx (now) disabled the clock and PX4IO_serial did not managed the clock

src/drivers/px4io/px4io_serial.cpp

@@ -217,6 +217,9 @@ PX4IO_serial::~PX4IO_serial()
 	stm32_unconfiggpio(PX4IO_SERIAL_TX_GPIO);
 	stm32_unconfiggpio(PX4IO_SERIAL_RX_GPIO);
 
+	/* Disable APB clock for the USART peripheral */
+    modifyreg32(STM32_RCC_APB2ENR, RCC_APB2ENR_USART6EN, 0);
+
 	/* and kill our semaphores */
 	sem_destroy(&_completion_semaphore);
 	sem_destroy(&_bus_semaphore);
@@ -239,12 +242,17 @@ PX4IO_serial::~PX4IO_serial()
 int
 PX4IO_serial::init()
 {
+
 	/* allocate DMA */
 	_tx_dma = stm32_dmachannel(PX4IO_SERIAL_TX_DMAMAP);
 	_rx_dma = stm32_dmachannel(PX4IO_SERIAL_RX_DMAMAP);
 	if ((_tx_dma == nullptr) || (_rx_dma == nullptr))
 		return -1;
 
+
+	/* Enable the APB clock for the USART peripheral */
+    modifyreg32(STM32_RCC_APB2ENR, 0, RCC_APB2ENR_USART6EN);
+
 	/* configure pins for serial use */
 	stm32_configgpio(PX4IO_SERIAL_TX_GPIO);
 	stm32_configgpio(PX4IO_SERIAL_RX_GPIO);
@@ -258,6 +266,7 @@ PX4IO_serial::init()
 	(void)rSR;
 	(void)rDR;
 
+
 	/* configure line speed */
 	uint32_t usartdiv32 = PX4IO_SERIAL_CLOCK / (PX4IO_SERIAL_BITRATE / 2);
 	uint32_t mantissa = usartdiv32 >> 5;