Fix priority setting of USART (serial needs tight timing).

example-usb-serial/sample.c

@@ -27,7 +27,7 @@ blk (void *arg)
   return NULL;
 }
 
-#define PRIO_USART     2
+#define PRIO_USART     4
 #define PRIO_CDC2USART 3
 #define PRIO_USART2CDC 3
 

example-usb-serial/usb-cdc.c

@@ -637,7 +637,7 @@ usb_rx_ready (uint8_t ep_num, uint16_t len)
 
 static void *cdc_main (void *arg);
 
-#define PRIO_CDC      4
+#define PRIO_CDC      2
 
 
 void