Fix issue with checking if already in host mode

Author: rechrtb

src/TinyUsbInterface.cpp

@@ -338,7 +338,7 @@ bool CoreUsbSetHostMode(bool hostMode, const StringRef& reply)
 		return false;
 	}
 
-	if (hostMode && digitalRead(UsbVbusDetect))
+	if (!CoreUsbIsHostMode() && digitalRead(UsbVbusDetect))
 	{
 		reply.printf("Unable to change to host mode, board plugged in to computer\n");
 		return false;