[bsp]Comment stm32f407 uart6

bsp/stm32f40x/drivers/board.h

@@ -43,7 +43,7 @@
 //#define RT_USING_UART1
 #define RT_USING_UART2
 //#define RT_USING_UART3
-#define RT_USING_UART6
+//#define RT_USING_UART6
 
 // <o> Console on USART: <0=> no console <1=>USART 1 <2=>USART 2 <3=> USART 3
 // 	<i>Default: 1