fix uart max len to 0xFFFF

Signed-off-by: huhui <huhui@sharkgulf.com>

Application/bsp/uart.c

@@ -101,7 +101,7 @@ static void shark_uart_rx(shark_uart_t *uart){
 					uart->rx_length -= 2; //skip crc
 					shark_uart_on_rx_frame(uart);
 				}
-				uart->rx_length = 0xFF;
+				uart->rx_length = 0xFFFF;
 				break;
 			case CH_ESC:
 				uart->escape = true;