[bsp][gd32]Fix the problem that uartv2 does not enable dma compilation error.

bsp/gd32/arm/libraries/gd32_drivers/drv_usart_v2.c

@@ -878,9 +878,8 @@ static void gd32_dma_config (struct rt_serial_device *serial, rt_ubase_t flag)
 static rt_err_t gd32_uart_control (struct rt_serial_device *serial, int cmd, void *arg)
 {
     struct gd32_uart *uart;
-#ifdef RT_SERIAL_USING_DMA
+
     rt_ubase_t ctrl_arg = (rt_ubase_t)arg;
-#endif
 
     RT_ASSERT(serial != RT_NULL);
     uart = rt_container_of(serial, struct gd32_uart, serial);
@@ -1027,8 +1026,10 @@ static rt_ssize_t gd32_transmit (struct rt_serial_device *serial, rt_uint8_t *bu
 
     if (uart->uart_dma_flag & RT_DEVICE_FLAG_DMA_TX)
     {
+#ifdef RT_SERIAL_USING_DMA
         _uart_dma_transmit(uart, buf, size);
         return size;
+#endif
     }
 
     gd32_uart_control(serial, RT_DEVICE_CTRL_SET_INT, (void *)tx_flag);
@@ -1041,11 +1042,7 @@ static const struct rt_uart_ops gd32_uart_ops =
     .control = gd32_uart_control,
     .putc = gd32_uart_putc,
     .getc = gd32_uart_getc,
-#ifdef RT_SERIAL_USING_DMA
     .transmit = gd32_transmit,
-#else
-    .transmit = RT_NULL,
-#endif
 };
 
 static void gd32_uart_get_config (void)

bsp/gd32/arm/libraries/gd32_drivers/drv_usart_v2.h

@@ -52,8 +52,8 @@ struct gd32_uart
         rt_size_t last_index;
         rt_sem_t sem_ftf;
     } dma;
-    rt_uint16_t uart_dma_flag;
 #endif
+    rt_uint16_t uart_dma_flag;
 };
 
 int rt_hw_usart_init(void);