Fix remotewakeup of PJRC stack(Fix #121)

- without this fix wakeup often fails
- keyboard can wakeup once or twice but fails after that

protocol/pjrc/usb.c

@@ -629,6 +629,7 @@ uint8_t usb_configured(void)
 void usb_remote_wakeup(void)
 {
     UDCON |= (1<<RMWKUP);
+    while (UDCON & (1<<RMWKUP));
 }