usb: fix freeze on sync commit for inactive pipes

Performing an asynchronous commit on an inactive pipe would yield
USB_COMMIT_INACTVE and *not* invoke the callback (as intended),
which usb_commit_sync() ignored, causing a freeze.

This issue appeared after a world switch, which (for reasons not yet
known) appear to fail the first writes until a commit, and that commit
would then hit an inactive pipe.

src/usb/pipes.c

@@ -401,7 +401,10 @@ void usb_commit_sync(int pipe)
 	while(rc == USB_COMMIT_BUSY);
 
 	/* Wait until the commit completes */
-	while(!flag) sleep();
+	if(rc == 0)
+	{
+		while(!flag) sleep();
+	}
 }
 
 /* usb_pipe_write_bemp(): Callback for the BEMP interrupt on a pipe */